8-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): February 8, 2018

FIRST FINANCIAL BANCORP.

(Exact name of registrant as specified in its charter)

Ohio	31-1042001
(State or other jurisdiction of incorporation or organization)	(I.R.S. employer identification number)

Commission file number: 001-34762

255 East Fifth Street, Suite 700, Cincinnati, Ohio 45202

(Address of principal executive offices and zip code)

Registrant's telephone number, including area code: (877) 322-9530

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

[ ] Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

[ ] Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

[ ] Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

[ ] Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Indicate by check mark whether the registrant is an emerging growth company as defined

in as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2

of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company¨

If an emerging growth company, indicate by check mark if the registrant has elected not

to use the extended transition period for complying with any new or revised financial accounting

standards provided pursuant to Section 13(a) of the Exchange Act. ¨

Form 8-KFirst Financial Bancorp.

Item 7.01    Regulation FD Disclosure.

The executive officers of First Financial Bancorp. intend to use the materials filed herewith, in whole or in part, in one or more meetings with investors and analysts. A copy of the investor presentation is attached hereto as Exhibit 99.1.

First Financial Bancorp. does not intend for this Item 7.01 or Exhibit 99.1 to be treated as “filed” for purposes of the Securities Exchange Act of 1934, as amended, or incorporated by reference into its filings under the Securities Act of 1933, as amended.

Item 9.01Financial Statements and Exhibits.

The following exhibit shall not be deemed to be “filed” for purposes of the Securities Exchange Act of 1934, as amended.

(d)Exhibits:

99.1 First Financial Bancorp. Investor Presentation.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

FIRST FINANCIAL BANCORP.

/s/ John M. Gavigan

John M. Gavigan

Senior Vice President and Chief Financial Officer

Date: February 8, 2018

EX-99.1

Investor Presentation Fourth Quarter 2017 EXHIBIT 99.1

2 Certain statements contained in this presentation which are not statements of historical fact constitute forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Such statements include, but are not limited to, certain plans, expectations, goals, projections and benefits relating to the transaction between the Company and MainSource, which are subject to numerous assumptions, risks and uncertainties. Words such as „„believes,‟‟ „„anticipates,‟‟ “likely,” “expected,” “estimated,” „„intends‟‟ and other similar expressions are intended to identify forward-looking statements but are not the exclusive means of identifying such statements. Examples of forward-looking statements include, but are not limited to, statements we make about (i) our future operating or financial performance, including revenues, income or loss and earnings or loss per share, (ii) future common stock dividends, (iii) our capital structure, including future capital levels, (iv) our plans, objectives and strategies, and (v) the assumptions that underlie our forward-looking statements. As with any forecast or projection, forward-looking statements are subject to inherent uncertainties, risks and changes in circumstances that may cause actual results to differ materially from those set forth in the forward-looking statements. Forward-looking statements are not historical facts but instead express only management‟s beliefs regarding future results or events, many of which, by their na ture, are inherently uncertain and outside of the management‟s control. It is possible that actual results and outcomes may differ, possibly materially, from the anticipated results or outcomes indicated in these forward-looking statements. Important factors that could cause actual results to differ materially from those in our forward-looking statements include the following, without limitation: (i) economic, market, liquidity, credit, interest rate, operational and technological risks associated with the Company‟s business; (ii) the effect of and changes in policies and laws or regulatory agencies, including the Dodd-Frank Wall Street Reform and Consumer Protection Act and other legislation and regulation relating to the banking industry; (iii) management‟s ability to effectively execute its business plans; (iv) mergers and acquisitions, including costs or difficulties related to the integration of acquired companies; (v) the Company‟s ability to comply with the terms of loss sharing agreements with the FDIC; (vi) the effect of changes in accounting policies and practices; (vii) changes in consumer spending, borrowing and saving and changes in unemployment; (viii) changes in customers‟ performance and creditworthiness; and (ix) the costs and effects of litigation and of unexpected or adverse outcomes in such litigation. Additional factors that may cause our actual results to differ materially from those described in our forward-looking statements can be found in the Form 10-K for the year ended December 31, 2016, as well as its other filings with the SEC, which are available on the SEC website at www.sec.gov. Statements concerning the potential merger of the Company and MainSource may also be forward-looking statements. Please refer to each of the Company‟s and MainSource‟s Annual Report on Form 10-K for the year ended December 31, 2016, as well as their other filings with the SEC, for a more detailed discussion of risks, uncertainties and factors that could cause actual results to differ from those discussed in the forward-looking statements. In addition to factors previously disclosed in reports filed by the Company and MainSource with the SEC, risks and uncertainties for the Company, MainSource and the combined company include, but are not limited to: the possibility that any of the anticipated benefits of the proposed Merger will not be realized or will not be realized within the expected time period; the risk that integration of MainSource's operations with those of the Company will be materially delayed or will be more costly or difficult than expected; the inability to close the Merger in a timely manner; diversion of management's attention from ongoing business operations and opportunities; the failure to satisfy other conditions to completion of the , including receipt of required regulatory and other approvals; the failure of the proposed Merger to close for any other reason; the challenges of integrating and retaining key employees; the effect of the announcement of the Merger on the Company‟s, MainSource‟s or the combined company's respective customer relationships and operating results; the possibility that the Merger may be more expensive to complete than anticipated, including as a result of unexpected factors or events; and general competitive, economic, political and market conditions and fluctuations. All forward-looking statements included in this filing are made as of the date hereof and are based on information available at the time of the filing. Except as required by law, neither the Company nor MainSource assumes any obligation to update any forward-looking statement. Forward Looking Statement Disclosure

3 About First Financial Bancorp Financial Performance MainSource Merger Update Appendix Presentation Contents

4 Company Overview NASDAQ: FFBC Overview Founded: 1863 Headquarters: Cincinnati, Ohio Banking Centers: 94 Assets: $8.9 billion Loans: $6.0 billion Deposits: $6.9 billion Wealth Mgmt: $2.7 billion AUM Lines of Business Commercial / Private Banking C&I, O-CRE, ABL, Equipment Finance, Treasury, Wealth Management Retail Banking Consumer, Mortgage, Small Business Investment Commercial Real Estate Commercial Finance Quick Service Restaurant, Insurance Agency Finance $ in millions except “per share” and where otherwise noted in the presentation www.bankatfirst.com $26.35 $26.15 $27.70 $27.45 $28.45 2.58% 2.60% 2.45% 2.48% 2.25% 4Q173Q172Q171Q174Q16 Share Price Dividend Yield

Central OH Loans $1.1 billion Loan Growth (Y-o-Y) 6.7% Deposits $0.5 billion Deposit Market Share #13 (0.8%) Banking Centers 5 Fortune 500 Companies 4 5 Our Markets Indianapolis Loans $0.5 billion Loan Growth (Y-o-Y) 16.6% Deposits $0.5 billion Deposit Market Share #13 (1.3%) Banking Centers 7 Fortune 500 Companies 3 Community Markets Loans $1.2 billion Loan Growth (Y-o-Y) (5.1%) Deposits $2.8 billion Banking Centers 36 Greater Cincinnati Loans $2.0 billion Loan Growth (Y-o-Y) 1.8% Deposits $2.6 billion Deposit Market Share #6 (2.0%) Banking Centers 46 Fortune 500 Companies 9

Proven Acquirer Two FDIC-assisted acquisitions totaling $2.5 billion in assets & generating a $343 million pre- tax bargain purchase gain (2009) Two branch acquisitions of 38 offices in Indiana & Ohio (2011) Three banks in Columbus, Ohio totaling $727 million in assets (2014) Oak Street Funding, specialty lender focused on the insurance industry, $243 million in assets (2015) Pending merger with MainSource Financial Group – close/integration in 1H 2018 Effective Operator 109 consecutive quarters of profitability through 4Q 2017 Replaced the runoff of ~ $2 billion of high yield covered loans Consolidated 78 banking centers in conjunction with efficiency efforts since 2009 Developed robust enterprise risk management & compliance programs, with board risk committee since 2010 6 Through the Cycle

Product expansions (since 2009) Specialty lending (~ $1.2 billion across Franchise, Oak Street, ABL, and Equipment Finance) Mobile banking & other technology enhancements for clients Re-entry into mortgage business (2010) 2017 originations of $229 million Wealth infrastructure improvements Investment model Real estate management, tax & insurance outsourcing Significant technology & infrastructure investments Continued expansion of risk management & compliance 7 Investments in our Business Mortgage Origination Platform Talent & Finance ERP Platform Enterprise Data Management Commercial & Consumer CRM

Proven & sustainable business model Well managed through the cycle Conservative operating philosophy Consistent profitability – 109 consecutive quarters Robust capital management Prudent steward of shareholders‟ capital Strong asset quality Well defined M&A strategy Selective markets, products & asset diversification Direct linkage between compensation and performance Short/long term incentive plans, management stock ownership targets 8 Invest with First Financial

9 1 Includes dividend reinvestment 2 Peer group includes KBW regional bank index peers 3 Based on stock price as of 12/29/2017 4 Based on stock price as of 01/26/2018 Invest with First Financial Total Shareholder Return1,2 117.5% 55.4% -4.9% 7.8% 117.5% 50.5% 1.4% 3.9% 148.4% 66.1% 6.6% 7.3% 5 Year 3 Year 1 Year YTD 2018 FFBC KBW Peer Median KBW Peer Top Quartile 3 4 3 3

10 Strategic Priorities Deliver long term top quartile shareholder returns Successfully integrate MainSource merger – achieve operational, cultural, & financial objectives Deploy capital in an opportunistic & risk-appropriate manner Invest in innovative solutions that enable our clients to bank with us on their terms Promote leadership & development within our communities Proactively develop leadership talent across the organization Achieve best-in-class compliance & risk management programs Remain vigilant in our credit philosophy & oversight Focused growth efforts in metropolitan markets Maintain process improvement & expense management discipline

11 About First Financial Bancorp Financial Performance MainSource Merger Update Appendix

12 4Q 2017 Highlights – 109th Consecutive Quarter of Profitability Total assets increased $135.2 million, to $8.9 billion, or 6.1% annualized, compared to the linked quarter. EOP loans increased $36.1 million, or 2.4% annualized, compared to the linked quarter. EOP deposits increased $169.0 million, or 10.0% annualized, compared to the linked quarter. EOP investment securities increased $46.8 million, or 9.2% annualized, compared to the linked quarter. Balance Sheet Profitability Asset Quality Income Statement Capital Noninterest income = $18.4 million. Noninterest expense = $82.9 million. Efficiency ratio = 88.2%. Adjusted efficiency ratio = 58.0%2 Effective tax rate of (119.5)%. Adjusted effective tax rate of 30.2%2 Net interest income = $75.6 million, a $5.1 million increase compared to the linked quarter. Net interest margin of 3.75% on a GAAP basis; 3.82% on a fully tax equivalent basis, a 25 bp increase from the linked quarter. Average earning assets grew 4.8% on an annualized basis. Net income = $24.8 million or $0.40 per diluted share. Adjusted net income = $27.7 million or $0.45 per diluted share2 Return on average assets = 1.13%. Adjusted return on average assets = 1.26%2 Return on average shareholders‟ equity = 10.70%. Adjusted return on average shareholders‟ equity = 11.95%2 Return on average tangible common equity = 13.85%1. Adjusted return on average tangible common equity = 15.46%2 Provision expense = $(0.2) million. Net charge offs = $0.3 million. NCOs / Avg. Loans = 0.02% annualized. Nonperforming Loans / Total Loans = 0.69%. Nonperforming Assets / Total Assets = 0.50%. ALLL / Nonaccrual Loans = 224.32%. ALLL / Total Loans = 0.90%. Classified Assets / Total Assets = 0.98%. Total capital ratio = 13.07%. Tier 1 capital ratio = 10.63%. Tangible common equity ratio = 8.30%. Tangible book value per share = $11.62. 1) See Appendix for non-GAAP reconciliation 2) See Slide 4 for Adjusted Earnings detail.

13 Profitability Net Income & EPS Return on Average Assets Return on Tangible Common Equity All dollars shown in millions, except per share data $24.8 $24.8 $22.7 $24.4 $23.3 $0.40 $0.40 $0.37 $0.39 $0.38 4Q173Q172Q171Q174Q16 Net Income EPS - diluted $8,732 $8,717 $8,583 $8,409 $8,360 1.13% 1.13% 1.06% 1.18% 1.11% 4Q173Q172Q171Q174Q16 Average Assets ROAA $711 $698 $680 $661 $653 13.85% 14.10% 13.42% 14.98% 14.19% 4Q173Q172Q171Q174Q16 Average Tangible Equity ROATCE

Adjusted Net Income* * See appendix for non-GAAP reconciliation All dollars shown in thousands, except per share amounts The table below lists certain items that we believe are significant to understanding our quarterly performance. 4Q 2017 As Reported Adjusted Net interest income $ 75,614 $ 75,614 Provision for loan and lease losses $ (205) $ (205) Noninterest income $ 18,382 $ 18,382 less: gains on sale of investment securities 19 A Total noninterest income $ 18,382 $ 18,363 Noninterest expense $ 82,898 $ 82,898 less: historic tax credit investment write-down 11,328 A less: merger-related expenses 8,444 A less: indemnification asset impairment 1 5,055 A less: charitable foundation contribution 3,000 A less: branch consolidation acitivities 577 A Total noninterest expense $ 82,898 $ 54,494 Income before income taxes $ 11,303 $ 39,688 Income tax expense $ (13,508) $ (13,508) plus: tax effect of adjustments (A) @ 35% statutory rate 9,935 plus: tax reform impact on DTLs & tax partnerships 8,191 plus: after-tax impact of historic tax credit write-down @ 35% 7,363 Total income tax expense $ (13,508) $ 11,981 Net income $ 24,811 $ 27,707 Net earnings per share - diluted $ 0.40 $ 0.45 1 - Impairment charge related to preliminary agreement to terminate FDIC loss sharing agreements. $0.45 $0.39 $0.36 $0.39 $0.38 4Q173Q172Q171Q174Q16 Adjusted EPS 1.26% 1.11% 1.06% 1.16% 1.11% 4Q173Q172Q171Q174Q16 Adjusted ROA 15.5% 13.9% 13.4% 14.7% 14.2% 4Q173Q172Q171Q174Q16 Adjusted ROTCE 58.0% 57.0% 59.7% 59.6% 57.4% 4Q173Q172Q171Q174Q16 Adjusted Efficiency Ratio 14

15 Net Interest Income / Net Interest Margin 1 Gross loans include loans held for sale & FDIC indemnification asset All dollars shown in millions Net Interest Income Average Loans1 Average Securities Average Deposits $75.6 $70.5 $68.5 $68.9 $70.2 3.82% 3.57% 3.56% 3.70% 3.71% 4Q173Q172Q171Q174Q16 Net Interest Income Net Interest Margin (FTE) $5,960 $5,911 $5,800 $5,748 $5,794 4.90% 4.71% 4.61% 4.64% 4.57% 4Q173Q172Q171Q174Q16 Gross Loans Loan Yield $2,020 $2,042 $2,035 $1,907 $1,817 2.90% 2.85% 2.77% 2.76% 2.58% 4Q173Q172Q171Q174Q16 Average Investment Securities Investment Securities Yield 24% 23% 23% 23% 24% 22% 22% 23% 23% 23% 37% 37% 37% 35% 32% 17% 18% 18% 19% 21% $6,840 $6,680 $6,570 $6,442 $6,557 0.54% 0.61% 0.53% 0.44% 0.37% 4Q173Q172Q171Q174Q16 Avg NIB Demand Avg IB Demand Avg Savings Avg Time Cost of Deposits

16 Net Interest Margin Net Interest Margin (FTE) 4Q17 NIM (FTE) Progression 3.58% 3.43% 3.41% 3.48% 3.48% 0.24% 0.14% 0.15% 0.22% 0.23% 3.82% 3.57% 3.56% 3.70% 3.71% 4Q173Q172Q171Q174Q16 Basic Margin (FTE) Loan Fees 3Q17 3.57% Earning asset mix 0.05% Interest recapture 0.02% Interest recapture from loans previously classified as nonaccrual Loan fees 0.10% Predominately loan prepayment fees Asset Drivers 0.17% Deposit Cost 0.06% Impact from deposit pricing strategies implemented in 3Q17 Funding Mix 0.02% Favorable mix shift toward lower cost deposits Liability Drivers 0.08% 4Q17 3.82%

17 Interest Rate Sensitivity Loan Portfolio – Floating Loan Growth (1) Sensitivity Trend (Up100, Up200) (3,4) 16% Y-o-Y growth in floating rate lending (1) 24% Y-o-Y growth in client derivatives (2) % of loans repricing: <=3 months 65% Securities portfolio duration – 2.9 years +100 scenario 3.6 years +200 scenario 4.0 years Non-maturity, interest bearing accounts modeled to increase 61 bps in an “Up 100” scenario (1) As defined by EOP loans repricing in three months or less. (2) As defined by client derivative notional balances. (3) Immediate parallel shifts across a 12 month horizon (4) EPS impact is calculated using the operating tax rate $3,368 $3,480 $3,639 $3,783 $3,908 58% 60% 62% 63% 65% 4Q16 1Q17 2Q17 3Q17 4Q17 Floating % of Gross Loans $0.020 $0.051 $0.049 $0.086 $0.084 $0.089 $0.108 $0.078 $0.176 $0.166 0.67% 1.64% 1.63% 2.65% 2.40% 2.96% 3.44% 2.60% 5.41% 4.73% 4Q16 1Q17 2Q17 3Q17 4Q17 Up100 Up200 Up100 Up200 EPS Impact Sensitivity

18 Loan Portfolio Loan Product Mix (EOP) Net Loan Change (Linked Quarter) * Includes residential mortgage, home equity, installment, & credit card loans. All dollars shown in millions Net Loan Change (Year-over-year) 33% 33% 33% 32% 33% 11% 12% 12% 12% 13% 30% 30% 30% 29% 29% 8% 7% 8% 8% 7% 18% 18% 18% 18% 18% $6,013 $5,977 $5,874 $5,754 $5,757 4Q173Q172Q171Q174Q16 Commercial & Leasing Owner Occupied CRE Investor CRE Construction Consumer Lending* $30.0 -$18.4 $3.1 -$14.9 $43.7 -$7.3 Commercial & Leasing Owner Occupied CRE Owner Occupied Construction Investor CRE Investor Construction Consumer Lending* $127.0 -$65.2 -$18.1 $127.7 $86.4 -$2.1 Commercial & Leasing Owner Occupied CRE Owner Occupied Construction Investor CRE Investor Construction Consumer Lending*

19 Loan Portfolio Loan Portfolio By Geography 1 Average Loan Size & Rate 2 Nationwide Lending Platforms 1 Includes loans held for sale. Excludes purchase accounting loan marks. 2 Average loan balances in $000s, rate represents weighted average coupon & does not include loan fees 3 Includes Oak Street, Franchise, shared national credits & other loans outside Ohio, Indiana, & Kentucky. $437 7% $533 9% $5,043 84% Oak Street Franchise All Other Loans $388 $412 $878 $1,060 $543 $117 $33 4.4% 4.3% 4.2% 5.2% 7.4% 4.0% 4.9% C&I* OOCRE* ICRE* Franchise Oak Street Mortgage Home EquityAverage Balance Weighted Average Rate * Ex.Franchise & OSF 3 $2,818 47% $1,451 24% $209 3% $1,558 26% Ohio Indiana Kentucky National Business 3

20 Loan Portfolio C&I Loans By Industry 1 CRE Loans By Collateral 2 1 Industry types included in Other representing greater than 1% of total C&I loans include Agriculture, Retail Trade, Public Administration, Other Services, Educational Services, Waste Management, Arts, and Transportation. 2 Collateral types included in Other representing greater than 1% of total CRE loans include Student Housing, Farmland, Manufacturing Facility, Strip Center, Real Estate IUB Other, Recreation Facility, Vacant Land Held for Development, Church/Related, School/Education, and Convenience Store. Finance and Insurance 24% Accommodation and Food Services 21% Manufacturing 12% Wholesale Trade 8% Real Estate and Rental and Leasing 6% Construction 4% Professional, Scientific, and Technical Services 4% Health Care and Social Assistance 4% Other 17% Total C&I Loans: $1.9B Retail 16% Residential, Multi Family 5+ 15% Office 13% Hotel/Motel 7% Restaurant 6% Warehouse 5% Industrial Facility 5% Residential, 1-4 Family 4% Medical Office 3% Nursing/Assisted Living 3% All others 23% Total CRE Loans: $3.0B

21 Investment Portfolio Total EOP investments of $2.1 billion Investment Portfolio / Total Assets = 23.1% Effective yield = 2.90% Portfolio duration = 2.9 years Portfolio Composition Portfolio Quality Agency, 56% AAA, 20% AA-, 4% BBB, 3% AA+, 3% FRB/FHLB Stock, 3% A+, 2% AA, 2% NR, 2% BBB+, 2% Other, 3% Commercial MBS 20% Asset-backed Securities 18% Agency CMOs 18% Agency Pass- through Securities 15% Municipal Securities 10% Non-Agency Pass- through Securities 7% Non-Agency CMOs 4% Corporate Securities 3% Regulatory Stock 3% U.S. Government Agency Debt 1% Other 1% U.S. Government Debt 0%

22 Asset Quality Nonperforming Assets / Total Assets Classified Assets / Total Assets Allowance / Total Loans Net Charge Offs & Provision Expense All dollars shown in millions $87.3 $94.3 $98.4 $114.6 $125.2 0.98% 1.08% 1.13% 1.34% 1.48% 4Q173Q172Q171Q174Q16 Classified Assets Classified Assets / Total Assets $44.4 $52.9 $62.7 $68.4 $54.3 0.50% 0.60% 0.72% 0.80% 0.64% 4Q173Q172Q171Q174Q16 NPAs NPAs / Total Assets $54.0 $54.5 $54.9 $56.3 $58.0 0.90% 0.91% 0.93% 0.98% 1.01% 4Q173Q172Q171Q174Q16 Allowance for Loan Losses ALLL / Total Loans $0.3 $3.3 $1.9 $2.0 $2.4 -$0.2 $3.0 $0.5 $0.4 $2.8 0.02% 0.22% 0.13% 0.14% 0.17% 4Q173Q172Q171Q174Q16 NCOs Provision Expense

23 Capital Tier 1 Common Equity Tangible Book Value Total Capital Tangible Common Equity All capital numbers are considered preliminary All dollars shown in millions $721.3 $705.2 $688.1 $669.7 $654.6 $11.62 $11.36 $11.07 $10.78 $10.56 4Q173Q172Q171Q174Q16 Tangible Book Value Tangible Book Value per Share $721.3 $705.2 $688.1 $669.7 $654.6 8.30% 8.25% 8.09% 8.05% 7.96% 4Q173Q172Q171Q174Q16 Tangible Book Value Tangible Common Ratio $929.1 $920.6 $905.2 $892.2 $881.2 13.07% 12.98% 13.05% 13.19% 13.10% 12.50% 4Q173Q172Q171Q174Q16 Total Capital Total Capital Ratio Target $755.7 $746.7 $731.0 $716.7 $703.9 10.63% 10.53% 10.54% 10.59% 10.46% 10.50% 4Q173Q172Q171Q174Q16 Tier 1 Common Equity Tier 1 Common Ratio Target

Outlook Taxes Full year 2018 loan growth expected to be in the mid-single digits on a percentage basis 1Q18 NIM (FTE) projected to be 3.70% – 3.75% Includes lower FTE adjustment due to tax reform 1Q18 loan fees likely to approximate 2Q17 & 3Q17 levels 1Q18 interest income will reflect 2 fewer days vs. 4Q17 Asset sensitive balance sheet, realization dependent on loan & deposit competition Noninterest expense base of approximately $51 million near-term, excluding one time expenses 4Q17 noninterest expense includes approximately $4 million related to higher incentive compensation and performance based 401(k) contribution Noninterest Expense Net Interest Margin Balance Sheet Preliminary full year 2018 effective tax rate of approximately 21% Will continue to refine as tax reform guidance becomes available 4Q17 adjusted earnings1 included $1.1 million net, after-tax benefit from historic tax credit investment realized during the period Credit Stable credit outlook Loan losses expected to revert to historical levels over time 1 See slide 4 for further detail. 24

25 About First Financial Bancorp Financial Performance MainSource Merger Update Appendix

Complementary Midwest Footprint 1) All branches located in Northwest Indiana and within the Chicago MSA Note: Deposit market share data shown pro forma as of 6/30/16 Source: SNL Financial Deposit Concentration By State OH, 56% IN, 41% KY, 3% FFBC Pro Forma Dollars in Millions Top 10 Pro Forma Markets MSA Rank Branches Deposits Cincinnati, OH 4 60 $2,884 Indianapolis, IN 13 18 789 Northwest IN ¹ 37 11 781 Louisvil le, KY 9 18 690 Columbus, IN 1 10 671 Dayton, OH 7 10 464 Columbus, OH 15 6 459 Greensburg, IN 1 5 345 Celina, OH 2 4 299 Bloomington, IN 3 3 290 Cincinnati, OH Indianapolis, IN FFBC (102) MSFG (101) Columbus, IN OH, 42% IN, 49% KY, 7% IL, 1% 26

Transaction Summary Fixed exchange ratio of 1.3875 shares of First Financial for each share of MainSource common stock 100% Stock Consideration $1.0 billion in aggregate transaction value¹ $38.99 purchase price per share¹ MainSource options will be exchanged for comparable First Financial options First Financial 63.4% / MainSource 36.6% of combined company4 The Board of Directors of the combined company will be comprised of 15 directors Composition will be proportionate with 9 First Financial board members & 6 from MainSource Claude Davis, current FFBC CEO, will be Executive Chairman for both holding company & bank Archie Brown, Jr., current MSFG CEO, will be President & CEO for both holding company & bank Expected in 1st Quarter 2018 Customary conditions to closing, including shareholder consent as well as receipt of all necessary regulatory approvals without any unduly burdensome conditions Consideration Option Treatment Pro Forma Ownership Board Composition Leadership Closing 1) Based on FFBC‟s closing price of $28.10 on July 25, 2017; calculation of total aggregate value includes in-the-money options and warrants 2) As of June 30, 2017; LTM earnings excludes $4.8mm of after-tax merger related charges for MSFG over the last twelve months 3) Based on MSFG‟s closing price of $33.81 on July 25, 2017 4) Calculated on a fully-diluted basis for First Financial and MainSource Headquarters Cincinnati, OH Valuation Multiples 2.72x tangible book value per share² 19.3x LTM earnings per share and 11.7x LTM earnings including fully phased-in after-tax cost savings² 15.3% market premium³ 27

Financial Impact & Assumptions Estimated $48 million; ~40% of MSFG‟s total noninterest expense base (~14.5% on a combined basis)5 ~40% of cost saves from consolidation of 45 – 50 banking centers ~75% of cost saves realized in first year post-close, 100% thereafter Gross credit mark on MSFG‟s loan portfolio of 1.00% or $31.9 million (net credit mark of 0.2%) Including MSFG‟s mark on PCI loans the gross transaction credit mark is $37.1 million, or 1.16% Cost Savings One-Time Expenses EPS Accretion TBV Value Impact Internal Rate of Return 6.4% in 2018 excl. transaction expenses, 11.1% in 2019 (first full year) 5.4% TBV dilution¹, earnback of 2.75 years using crossover method², 3.15 years using simple method³ 18% IRR, above internal targets Credit Mark Total restructuring costs of ~$63 million5 1) See Appendix for non-GAAP reconciliation 2) Based on when pro forma tangible book value per share crosses over and begins to exceed projected standalone FFBC tangible book value per share 3) Based on dilution to tangible book value per share at close divided by earnings per share accretion in 2019 4) All dollar amounts shown pre-tax except reduction in Fed dividend payments 5) Estimated cost savings and restructuring charges may be refined as the companies work through integration planning $12 million combined annual interchange fee revenue loss due to Durbin Phase in – 50% in 2019, 100% thereafter $2 million additional annual expenses from heightened regulatory / compliance costs Phase in – 50% in 2018, 100% thereafter $500 thousand reduction in dividend payments on Federal Reserve Bank capital stock due to FAST Act Phase in – 50% in 2018, 100% thereafter $46.0 million CDI created (1.5% of core deposits), amortized over 9 years using sum of years digits $5.1 million write-down on MSFG‟s TruPS, amortized through earnings over 16.3 years $4.5 million write-down on MSFG‟s CDs & FHLB advances, amortized through earnings over 5.25 years Regulatory Adjustments4 Other Purchase Accounting Adjustments 28

14.1% 14.1% 15.8% 0.0% 4.0% 8.0% 12.0% 16.0% 20.0% FFBC LTM 6/30/17 MSFG LTM 6/30/17 Pro Forma 2019 1.1 % 1.17% 1.30% 0.00% 0.25% 0.50% 0.75% 1.00% 1.25% 1.50% FFBC LTM 6/30/17 MSFG LTM 6/30/17 Pro Forma 2019 Capital & Profitability Total Assets Total Risk Based Capital ROAA⁴ ROATCE⁴ Tang. Common Equity / Tang. Assets⁴ 8.1% 8.3% 8.2% 5.0% 6.0% 7.0% 8.0% 9.0% 10.0% 11.0% 12.0% FFBC 6/3 /17 MSFG 6/30/17 Pro Forma at Close Tier 1 Common Ratio 10.5% 11.2% 10.8% 5.0% 7. 9.0% 11.0% 13.0% 15.0% FFBC 6/30/17 MSFG 6/30/17 Pro Forma at Close 1) Pro forma as of 6/30/17; excludes purchase accounting marks & growth 2) Pro forma ratio at closing, 3/31/18; includes all purchase accounting adjustments 3) Pro forma ratio for full year ending 12/31/19; includes all purchase accounting adjustments & assumes 100% Durbin impact 4) See Appendix for non-GAAP reconciliation 5) Core LTM Ratios adjusted for merger-related expenses & FHLB prepayment penalty Source: SNL Financial; Company documents 13.1% 13.3% 13.0% 6.0% 8.0% 10.0% 12.0% 14.0% 16.0% FFBC 6/30 17 MSFG 6/30/17 Pro Forma at Close $8,710 $4,590 $13,300 $0 $3,000 $6,000 $9,000 $12,000 $15,000 FFBC 6/30/17 MSFG 6/30/17 Pro Forma 6/30/17 5 5 29 2 3 3 1 2 2

MainSource Merger Update Regulatory & Shareholder Approval Merger Integration Financial Considerations Shareholders approved on December 4, 2017 Regulatory applications completed – September 2017 Phase 1 substantially complete Technology Assessment – Complete Organization Structure / Staffing Assessment – Complete Contract Negotiations / Terminations – In Process; mostly complete Phase 2 ongoing Cross-company action teams actively engaged across all functional areas Formed First Financial Foundation in December 2017 $3 million contribution to First Financial Foundation in 4Q 2017 Community Investment Plan No significant changes to financial considerations at this time Merger Timeline Expected close 1Q 2018 Expected conversion mid to late 2Q 2018 30

Branch Divestiture Letter of Agreement with United States Department of Justice to divest five branch locations to resolve competitive concerns Includes $125 million in loans, $160mm in deposits and all personal property associated with the branches 4 MainSource Bank branch locations in Columbus, Indiana 529 Washington Street, Columbus, IN 47201 803 Washington Street, Columbus, IN 47201 (Drive-thru) 1901 25th Street, Columbus, IN 47201 2310 W Jonathan Moore Pike, Columbus, IN 47202 1 MainSource Bank branch location in Greensburg, Indiana 304 E 10th Street, Greensburg, IN 47240 Expected to consummate within 180 days following completion of the merger 31

MSFG 4Q 2017 Highlights Profitability Net Interest Income & Net Interest Margin Income Statement Balance Sheet Asset Quality Capital  Net income = $16.6 million, or $14.4 million excluding non-operating items(1)  EPS = $0.64 per diluted share, or $0.55 per diluted share excluding non-operating items(1)  Return on average assets = 1.43%, or 1.24% excluding non-operating items(1)  Return on average shareholders’ equity = 12.5%, or 10.9% excluding non-operating items(1)  Return on average tangible common equity = 17.5%, or 15.2% excluding non-operating items(1)  Net interest income = $37.7 million, a $0.3 million increase compared to the linked quarter  Net interest margin of 3.78% on a fully tax equivalent basis  Purchase accounting marks added nineteen (19) basis points to the net interest margin  Noninterest income = $13.8 million  Noninterest expense = $31.7 million, or $31.3 million excluding non-operating expenses(1)  Efficiency ratio = 59.2%, or 58.5% excluding non-operating items(1)  Effective tax rate of 13.6%, 26.7% excluding the effect of tax reform  EOP loans increased $15 million on a linked quarter basis, or 2% annualized growth  Provision expense = $550K. Net charge offs = $550K. NCOs / Avg. Loans = 0.07% annualized  Nonperforming Assets (w/TDRs) / Total Assets = 0.45%  ALLL / Nonperforming Loans = 139.5%. ALLL / Total Loans = 0.74%  Total capital ratio = 13.6%  Tier 1 capital ratio = 12.9%  Tangible common equity ratio = 8.5%  Tangible book value per common share = $14.93 (1) Non-operating items include $0.3 million in merger-related expenses, net of tax and a $2.5 million income tax benefit due to tax reform. 32

33 About First Financial Bancorp Financial Performance MainSource Merger Update Appendix

34 Appendix: Non-GAAP to GAAP Reconciliation Net interest income and net interest margin - fully tax equivalent Dec. 31, Sep. 30, June 30, Mar. 31, Dec. 31, Dec. 31, Dec. 31, 2017 2017 2017 2017 2016 2017 2016 Net interest income 75,614$ 70,479$ 68,520$ 68,932$ 70,166$ 283,545$ 272,671$ Tax equivalent adjustment 1,387 1,353 1,294 1,225 1,077 5,259 4,215 Net interest income - tax equivalent 77,001$ 71,832$ 69,814$ 70,157$ 71,243$ 288,804$ 276,886$ Average earning assets 8,005,100$ 7,989,969$ 7,855,564$ 7,695,717$ 7,630,148$ 7,887,718$ 7,524,233$ Net interest margin* 3.75 % 3.50 % 3.50 % 3.63 % 3.66 % 3.59 % 3.62 % Net interest margin (fully tax equivalent)* 3.82 % 3.57 % 3.56 % 3.70 % 3.71 % 3.66 % 3.68 % Three months ended YTD * Margins are calculated using net interest income annualized divided by average earning assets. The earnings press release and accompanying presentation include certain non-GAAP ratios, such as net interest income-tax equivalent. The tax equivalent adjustment to net interest income recognizes the income tax savings when comparing taxable and tax-exempt assets and assumes a 35% tax rate. Management believes that it is a standard practice in the banking industry to present net interest margin and net interest income on a fully tax equivalent basis. Therefore, management believes these measures provide useful information to investors by allowing them to make peer comparisons. Management also uses these measures to make peer comparisons.

35 Appendix: Non-GAAP to GAAP Reconciliation Additional non-GAAP ratios Dec. 31, Sep. 30, June 30, Mar. 31, Dec. 31, Dec. 31, Dec. 31, (Dollars in thousands, except per share data) 2017 2017 2017 2017 2016 2017 2016 Net income (a) 24,811$ 24,826$ 22,736$ 24,414$ 23,294$ 96,787$ 88,526$ Average total shareholders' equity 920,194 908,057 889,604 871,215 863,509 897,431 844,784 Less: Goodw ill and other intangibles (209,379) (209,730) (210,045) (210,324) (210,625) (209,379) (210,625) Average tangible equity (b) 710,815 698,327 679,559 660,891 652,884 688,052 634,159 Total shareholders' equity 930,664 914,954 898,117 880,065 865,224 930,664 865,224 Less: Goodw ill and other intangibles (209,379) (209,730) (210,045) (210,324) (210,625) (209,379) (210,625) Ending tangible equity (c) 721,285 705,224 688,072 669,741 654,599 721,285 654,599 Total assets 8,896,923 8,761,689 8,710,042 8,531,170 8,437,967 8,896,923 8,437,967 Less: Goodw ill and other intangibles (209,379) (209,730) (210,045) (210,324) (210,625) (209,379) (210,625) Ending tangible assets (d) 8,687,544 8,551,959 8,499,997 8,320,846 8,227,342 8,687,544 8,227,342 Risk-w eighted assets (e) 7,134,085 7,090,714 6,936,665 6,765,336 6,728,737 7,134,085 6,728,737 Total average assets 8,731,956 8,716,917 8,582,961 8,409,071 8,359,912 8,611,403 8,251,703 Less: Goodw ill and other intangibles (209,379) (209,730) (210,045) (210,324) (210,625) (209,379) (210,625) Average tangible assets (f) 8,522,577$ 8,507,187$ 8,372,916$ 8,198,747$ 8,149,287$ 8,402,024$ 8,041,078$ Ending shares outstanding (g) 62,069,087 62,061,465 62,141,071 62,134,285 61,979,552 62,069,087 61,979,552 Ratios Return on average tangible shareholders' equity (a)/(b) 13.85% 14.10% 13.42% 14.98% 14.19% 14.07% 13.96% Ending tangible equity as a percent of: Ending tangible assets (c)/(d) 8.30% 8.25% 8.09% 8.05% 7.96% 8.30% 7.96% Risk-w eighted assets (c)/(e) 10.11% 9.95% 9.92% 9.90% 9.73% 10.11% 9.73% Average tangible equity as a percent of average tangible assets (b)/(f) 8.34% 8.21% 8.12% 8.06% 8.01% 8.19% 7.89% Tangible book value per share (c)/(g) 11.62$ 11.36$ 11.07$ 10.78$ 10.56$ 11.62$ 10.56$ Three months ended YTD The earnings press release and accompanying presentation include certain non-GAAP ratios. These ratios include: (1) Return on average tangible shareholders' equity; (2) Ending tangible shareholders' equity as a percent of ending tangible assets; (3) Ending tangible shareholders' equity as a percent of risk-w eighted assets; (4) Average tangible shareholders' equity as a percent of average tangible assets; and (5) Tangible book value per share. The Company considers these critical metrics w ith w hich to analyze banks. The ratios have been included in the earnings press release to facilitate a better understanding of the Company's capital structure and f inancial condition.

36 Appendix: Non-GAAP to GAAP Reconciliation Additional non-GAAP ratios As Reported Adjusted As Reported Adjusted As Reported Adjusted As Reported Adjusted As Reported Adjusted Net interest income (f) 75,614$ 75,614$ 70,479$ 70,479$ 68,520$ 68,520$ 68,932$ 68,932$ 70,166$ 70,166$ Provision for loan and lease losses (205) (205) 2,953 2,953 467 467 367 367 2,761 2,761 plus: provision expense adjustment 799 Noninterest income 18,382 18,382 22,942 22,942 17,454 17,454 17,364 17,364 16,946 16,946 less: gains from the redemption of off balance sheet securitizations 5,764 less: tax related adjustment to a limited partnership investment (119) less: gains on sale of investment securities 19 275 838 516 Total noninterest income (g) 18,382 18,363 22,942 16,903 17,454 16,735 17,364 16,848 16,946 16,946 Noninterest expense 82,898 82,898 54,443 54,443 51,556 51,556 51,045 51,045 50,163 50,163 less: severance expense 3,818 533 less: charter conversion expenses 86 less: historic tax credit investment write-down 11,328 less: merger-related expenses 8,444 800 less: indemnification asset impairment 1 5,055 less: charitable foundation contribution 3,000 less: branch consolidation acitivities 577 154 (92) Total noninterest expense (e) 82,898 54,494 54,443 49,825 51,556 50,869 51,045 51,137 50,163 50,077 Income before income taxes (i) 11,303 39,688 36,025 35,403 33,951 33,919 34,884 34,276 34,188 34,274 Income tax expense (13,508) (13,508) 11,199 11,199 11,215 11,215 10,470 10,470 10,894 10,894 plus: tax effect of adjustments 9,935 (178) (11) (213) 31 plus: tax reform impact on DTLs & tax partnerships 8,191 plus: after-tax impact of historic tax credit write-down @ 35% 7,363 - Total income tax expense (h) (13,508) 11,981 11,199 11,021 11,215 11,204 10,470 10,257 10,894 10,925 Net income (a) 24,811$ 27,707$ 24,826$ 24,382$ 22,736$ 22,715$ 24,414$ 24,019$ 23,294$ 23,349$ Average diluted shares (b) 62,132 62,132 62,190 62,190 62,234 62,234 62,140 62,140 62,081 62,081 Average assets (c) 8,731,956 8,731,956 8,716,917 8,716,917 8,582,961 8,582,961 8,409,071 8,409,071 8,359,912 8,359,912 Average shareholders' equity 920,194 920,194 908,057 908,057 889,604 889,604 871,215 871,215 863,509 863,509 Less: Goodwill and other intangibles (209,379) (209,379) (209,730) (209,730) (210,045) (210,045) (210,324) (210,324) (210,625) (210,625) Average tangible equity (d) 710,815 710,815 698,327 698,327 679,559 679,559 660,891 660,891 652,884 652,884 1 - Impairment charge related to preliminary agreement to terminate FDIC loss sharing agreements. Ratios Net earnings per share - diluted (a)/(b) 0.40$ 0.45$ 0.40$ 0.39$ 0.37$ 0.37$ 0.39$ 0.40$ 0.38$ 0.39$ Return on average assets - (a)/(c) 1.13% 1.26% 1.13% 1.11% 1.06% 1.06% 1.18% 1.16% 1.11% 1.11% Return on average tangible shareholders' equity - (a)/(d) 13.85% 15.46% 14.10% 13.85% 13.42% 13.41% 14.98% 14.74% 14.19% 14.23% Efficiency ratio - (e)/((f)+(g)) 88.19% 57.99% 58.28% 57.02% 59.97% 59.67% 59.15% 59.61% 57.58% 57.49% Effective tax rate - (h)/(i) -119.5% 30.2% 31.1% 31.1% 33.0% 33.0% 30.0% 29.9% 31.9% 31.9% (Dollars in thousands, except per share data) 4Q164Q17 3Q17 2Q17 1Q17

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