Exhibit 99.1

Old Second Bancorp, Inc.	For Immediate Release
(Nasdaq: OSBC)	October 20, 2006

Contact:	J. Douglas Cheatham
	Chief Financial Officer
	(630) 906-5484

Old Second Bancorp, Inc. Announces Third Quarter Earnings

AURORA, Illinois — Old Second Bancorp, Inc. (Nasdaq: OSBC) today announced third quarter earnings of $0.37 per diluted share, on earnings of $4.9 million. Diluted earnings per share were down from the third quarter of 2005, in which the Company earned $0.52 per diluted share on earnings of $7.2 million. Earnings for the first nine months of 2006 were $1.28 per diluted share, on $17.4 million in net income, compared with $1.46 per diluted share in the same period of 2005, on earnings of $19.9 million. The Company is in the process of distributing the assets of its defined benefit pension plan after terminating the plan in December of 2005. A loss on settlement of the benefit obligations relating to the termination of $1,001,000 was recorded in the third quarter of 2006. The loss related to the termination of the defined benefit pension plan was $1,358,000 for the first nine months of 2006. The liabilities are expected to exceed assets at the time of final distribution of all benefits by approximately $250,000. A contribution of the remaining shortfall amount is required to be made before the defined benefit plan is liquidated, which is anticipated to be in the fourth quarter of 2006. Generally, for the year to date period, balance sheet growth and an increase in noninterest income were offset by a lower net interest margin, a higher provision for loan losses, a decline in mortgage banking activity, and increased facility and related costs associated with branch expansion into new markets.

Net interest income declined in the first nine months of 2006, from $55.0 million in 2005 to $53.5 million in 2006. Third quarter net interest income declined from $18.8 million in 2005, to $17.3 million in 2006. For both the quarter and year to date periods, the growth in earning assets was offset by a lower net interest margin. Average earning assets grew $128.0 million or 6.14% from the first nine months of 2005 to the first nine months of 2006. In the same period, however, the net interest margin declined from 3.66% in 2005 to 3.37% in 2006.

On a year to date comparative basis, the average tax-equivalent yield on earning assets increased from 5.73% in 2005 to 6.49% in 2006, which was a 76 basis point increase. During the same nine-month period, however, the cost of funds increased from 2.40% to 3.55%, or 115 basis points. Changes in funding composition had a significant affect on increasing interest costs and lowering the net interest margin. The average balances of lower cost sources of funds such as interest-bearing transaction accounts and savings accounts declined $26.1 million, or 3.2% from the first nine months of 2005 to the first nine months of 2006. Noninterest-bearing deposits increased by a nominal amount while the aggregate categories of higher-cost sources of funds such as time deposits, repurchase agreements and short-term borrowing increased $170.4 million, or 17.7%.

The Company recorded a provision for loan losses of $400,000 in the third quarter of 2006, versus $450,000 in the third quarter of 2005. In the first nine months of 2006, the Company provided $1,244,000 compared with $813,000 in the first nine months of 2005, an increase of $431,000. Loan portfolio quality remained strong through the third quarter of 2006, and the amount of charge-offs continued at the Company’s low level. Management performed quantitative and

qualitative analysis of the allowance for loan losses and determined that the amount reported as of September 30, 2006, was appropriate. Despite the general decline in nonperforming assets in 2006, management increased the allowance for loan losses in 2006 to address concerns associated with the commercial real estate market and the large concentration held by the Company. The ratio of the allowance for loan losses to nonperforming loans was 363% as of September 30, 2006, compared with 324% as of September 30, 2005. Nonperforming loans were $4.5 million as of September 30, 2006, and $4.9 million as of September 30, 2005. Net charge-offs were $149,000 in the third quarter of 2006 and $136,000 in the third quarter of 2005. On a year to date basis, net charge-offs were $229,000 in the first nine months of 2006 and $469,000 in the first nine months of 2005.

Noninterest income was $6.9 million during the third quarter of 2006 and $7.4 million during the third quarter of 2005, a decrease of $500,000, or 6.8%. This decrease was primarily due to a reduction in mortgage banking income, including gains on sales of mortgage loans, secondary market fees, and servicing income, which declined $698,000, or 37.1%, from the third quarter of 2005 to the third quarter of 2006. For the year to date, mortgage-banking income was down $1,614,000, or 30.1%, from the first nine months of 2005 to the first nine months of 2006. Higher borrowing costs associated with an increased interest rate environment resulted in a decline in mortgage loan demand and related mortgage banking income. Other income decreased $146,000, or 9.7%, from the third quarter of 2005, to $1.4 million in the third quarter of 2006. Other income increased $80,000, or 2.0%, from the first nine months of 2005 to $4.2 million for the first nine months of 2006.

Trust income was up $127,000, or 8.0%, from the third quarter of 2005 to the third quarter of 2006, to $1.7 million. Trust income was $5.5 million in the first nine months of 2006, an increase of $636,000, or 13.1%, from the first nine months of 2005. Increases in trust income for both the quarter and the year to date period were primarily associated with estate fees. There were no security sales in the third quarter of 2006 or 2005, while securities gains totaled $418,000 in the first nine months of 2006, compared with a $5,000 loss in the first nine months of 2005. Bank owned life insurance (“BOLI”) income increased from $218,000 to $483,000 in the third quarter, and from $652,000 to $1,444,000 on a year to date basis, when comparing 2006 and 2005, as a result of BOLI purchases.

Noninterest expense was $17.2 million during the third quarter of 2006, an increase of $2,127,000, or 14.1%, from $15.1 million in the third quarter of 2005. Noninterest expense was $49.0 million during the first nine months of 2006, an increase of $3,513,000, or 7.7%, from $45.5 million in the first nine months of 2005. Salaries and benefits expense was $9.2 million during the third quarter of 2006, an increase of $413,000, or 4.7% from $8.8 million in the third quarter of 2005. In the first nine months of the year, salaries and benefits were $27.3 million in 2006 and $26.9 million in 2005, an increase of $413,000 or 1.5%.

Net occupancy and furniture and equipment expenses increased $204,000 from the third quarter of 2005 to the third quarter of 2006, or 8.5%. Net occupancy and furniture and equipment expenses increased $891,000 from the first nine months of 2005 to the first nine months of 2006, or 13.8%. The increase in the year to date period is due, in part, to a reduction in the estimated accrual for occupancy related expenses in the first nine months of 2005. As the Company has expanded into and developed new markets, related facility expenses have increased. Two new branches opened in the first quarter of 2005, one branch opened in the first quarter of 2006 and two additional branch locations opened in the third quarter of 2006. Other expense increased

$496,000, or 15.0%, from the third quarter of 2005, to $3.8 million in the third quarter of 2006. Other expenses increased $701,000, or 6.6% from the first nine months of 2005 to $11.3 million in the first nine months of 2006. Increases in other expense for both the quarter and the year to date basis, when comparing 2006 and 2005 primarily related to loan expenditures, amortization of mortgage servicing rights, and new employee recruitment fees.

The provision for income tax as a percentage of pretax income decreased from 33.0% as of the third quarter of 2005 to 25.0% as of the third quarter of 2006. Income tax as a percentage of pretax income decreased from 32.7% for the first nine months of 2005 to 29.3% for the first nine months of 2006. The percentage of pretax dollars used for income tax expense was reduced primarily due to the increased level of BOLI detailed in the noninterest income discussion above, and a new tax planning strategy that was implemented at the end of the third quarter of 2006.

Total assets were $2.41 billion as of September 30, 2006, compared with $2.37 billion as of December 31, 2005. Loans grew $81.0 million during the first nine months of 2006, while securities available for sale declined $25.0 million. Real estate loans to the commercial, construction and residential sectors increased $43.2 million (7.3%), $14.2 million (3.9%) and $30.5 (5.5%) respectively, in the first nine months of 2006.

Total deposits increased $82.6 million during the first nine months of 2006. Noninterest bearing and savings deposits decreased $5.7 million (2.2%) and $11.4 million (9.7%) respectively. At the same time, NOW and money market accounts increased $22.5 million (9.2%) and $7.5 million (1.7%) respectively. Year to date, time deposits increased $69.7 million, or 8.0%, from $876.1 million to $945.8 million. Pricing and sales strategies targeted the 2006 growth in NOW and money market accounts. Depositors also continued to migrate into term certificates of deposits to lock in rates from the rising interest rate environment. Increases in interest-bearing transaction account pricing and the continued shift into certificates of deposit resulted in a higher cost of funds and had a negative impact on the net interest margin.

Non-GAAP Presentations: Management uses certain non-GAAP ratios to evaluate and measure the Company’s performance. Management presents a net interest margin calculation. The net interest margin is calculated by dividing net interest income on a tax equivalent basis by average earning assets for the period. Management believes this measure provides investors with information regarding balance sheet profitability. Management also presents an efficiency ratio that is non-GAAP. The efficiency ratio is calculated by dividing adjusted non-interest expense by the sum of net interest income on a tax equivalent basis and adjusted non-interest income. Management believes this measure provides investors with information regarding the Company’s operating efficiency and how management evaluates performance internally. The tables provide a reconciliation of each non-GAAP measure to the most comparable GAAP equivalent.

Forward Looking Statements: This report may contain forward-looking statements. Forward looking statements are identifiable by the inclusion of such qualifications as expects, intends, believes, may, likely or other indications that the particular statements are not based upon facts but are rather based upon the company’s beliefs as of the date of this release. Actual events and results may differ significantly from those described in such forward looking statements, due to changes in the economy, interest rates or other factors. Additionally, all statements in this document, including forward-looking statements, speak only as of the date they are made, and the Company undertakes no obligation to update any statement in light of new information or future events. For additional information concerning the Company and its business, including

other factors that could materially affect the Company’s financial results, please review our filings with the Securities and Exchange Commission, including the Company’s Form 10-K for 2005.

Financial Highlights (unaudited)
In thousands, except share data

	Three Months Ended						Year to Date
	September 30,						September 30,
	2006			2005			2006			2005
Summary Income Statement:
Net interest income	$	17,299		$	18,849		$	53,524		$	54,959
Provision for loan losses	400			450			1,244			813
Noninterest income	6,874			7,374			21,314			20,951
Noninterest expense	17,177			15,050			48,972			45,459
Income taxes	1,648			3,541			7,203			9,697
Net income	4,948			7,182			17,419			19,941

Key Ratios (annualized):
Return on average assets	0.82		%	1.25		%	0.98		%	1.20		%
Return on average equity	13.17		%	19.30		%	15.11		%	18.67		%
Net interest margin (tax equivalent)	3.21		%	3.62		%	3.37		%	3.66		%
Efficiency ratio	68.96		%	55.82		%	63.58		%	58.28		%
Tangible capital to tangible assets	6.32		%	6.21		%	6.32		%	6.21		%
Total capital to risk weighted assets	10.63		%	10.39		%	10.63		%	10.39		%
Tier 1 capital to risk weighted assets	9.78		%	9.55		%	9.78		%	9.55		%
Tier 1 capital to average assets	7.84		%	7.89		%	7.84		%	7.89		%

Per Share Data:
Basic earnings per share	$	0.37		$	0.53		$	1.30		$	1.48
Diluted earnings per share	$	0.37		$	0.52		$	1.28		$	1.46
Dividends declared per share	$	0.14		$	0.13		$	0.41		$	0.38
Book value per share	$	11.74		$	10.97		$	11.74		$	10.97
Tangible book value per share	$	11.57		$	10.78		$	11.57		$	10.78
Ending number of shares outstanding	13,166,798			13,497,889			13,166,798			13,497,889
Average number of shares outstanding	13,279,824			13,497,889			13,443,668			13,482,340
Diluted average shares outstanding	13,451,345			13,690,895			13,619,125			13,675,603

End of Period Balances:
Loans	$	1,785,406		$	1,670,650		$	1,785,406		$	1,670,650
Deposits	2,017,831			1,946,854			2,017,831			1,946,854
Stockholders’ equity	154,554			148,123			154,554			148,123
Total earning assets	2,245,252			2,205,079			2,245,252			2,205,079
Total assets	2,412,664			2,346,745			2,412,664			2,346,745

Average Balances:
Loans	$	1,762,217		$	1,636,937		$	1,741,232		$	1,597,319
Deposits	1,983,937			1,915,232			1,977,870			1,862,185
Stockholders’ equity	149,057			147,625			154,146			142,785
Total earning assets	2,225,966			2,144,970			2,212,868			2,084,821
Total assets	2,386,459			2,279,134			2,370,065			2,212,875

Financial Highlights, continued (unaudited)
In thousands, except share data

	Three Months Ended						Year to Date
	September 30,						September 30,
	2006			2005			2006			2005
Asset Quality
Charge-offs	$	261		$	156		$	605		$	893
Recoveries	112			20			376			424
Net charge-offs	$	149		$	136		$	229		$	469
Provision for loan losses	$	400		$	450		$	1,244		$	813
Allowance for loan losses to loans	0.92		%	0.95		%	0.92		%	0.95		%

	September 30,						December 31,
	2006			2005			2005

Nonaccrual loans	$	3,162		$	4,795		$	3,845
Restructured loans	—			—			—
Loans past due 90 days	1,343			88			2,752
Nonperforming loans	4,505			4,883			6,597
Other real estate	83			576			251
Nonperforming assets	$	4,588		$	5,459		$	6,848

Major Classifications of Loans
Commercial and industrial	$	168,468		$	166,443		$	168,314
Real estate - commercial	633,554			581,231			590,328
Real estate - construction	376,097			327,999			361,859
Real estate - residential	581,325			554,757			550,823
Installment	27,877			42,636			35,236
	1,787,321			1,673,066			1,706,560
Unearned origination fees, net	(1,915		)	(2,416		)	(2,178		)
	$	1,785,406		$	1,670,650		$	1,704,382

Major Classifications of Deposits
Noninterest bearing	$	258,403		$	253,587		$	264,124
Savings	106,402			120,237			117,849
NOW accounts	267,247			236,618			244,727
Money market accounts	439,992			483,330			432,452
Certificates of deposits of less than $100,000	566,864			547,446			554,618
Certificates of deposits of $100,000 or more	378,923			305,636			321,508
	$	2,017,831		$	1,946,854		$	1,935,278

Old Second Bancorp, Inc.
Consolidated Balance Sheets
(In thousands)

	September 30,			December 31,
	2006			2005
Assets
Cash and due from banks	$	58,758		$	65,010
Interest bearing deposits with banks	117			105
Cash and cash equivalents	58,875			65,115
Securities available for sale	445,437			470,431
Federal Home Loan Bank and Federal Reserve Bank stock	8,783			8,418
Loans held for sale	5,509			11,397
Loans	1,785,406			1,704,382
Allowance for loan losses	16,344			15,329
Net loans	1,769,062			1,689,053
Premises and equipment, net	45,736			42,485
Other real estate owned	83			251
Mortgage servicing rights, net	2,900			2,271
Goodwill, net	2,130			2,130
Core deposit intangible assets, net	89			355
Bank owned life insurance	43,071			41,627
Accrued interest and other assets	30,989			34,297
Total assets	$	2,412,664		$	2,367,830

Liabilities
Deposits:
Demand	$	258,403		$	264,124
Savings, NOW, and money market	813,641			795,028
Time	945,787			876,126
Total deposits	2,017,831			1,935,278
Securities sold under repurchase agreements	42,506			57,625
Other short-term borrowings	133,724			171,825
Junior subordinated debentures	31,625			31,625
Notes payable	13,375			3,200
Accrued interest and other liabilities	19,049			16,015
Total liabilities	2,258,110			2,215,568

Stockholders’ Equity
Common stock	16,634			16,592
Additional paid-in capital	14,758			13,746
Retained earnings	188,768			176,824
Accumulated other comprehensive loss	(3,310		)	(4,562		)
Treasury stock	(62,296		)	(50,338		)
Total stockholders’ equity	154,554			152,262
Total liabilities and stockholders’ equity	$	2,412,664		$	2,367,830

Old Second Bancorp, Inc.
Consolidated Statements of Income
(In thousands, except share data)

	Three Months Ended				Year to Date
	September 30,				September 30,
	2006		2005		2006		2005
Interest and Dividend Income
Loans, including fees	$	31,867	$	26,413	$	91,544	$	74,373
Loans held for sale	127		185		353		547
Securities:
Taxable	3,167		3,193		9,518		8,785
Tax-exempt	1,258		1,266		3,749		3,597
Federal funds sold	2		4		5		7
Interest bearing deposits	1		1		3		2
Total interest and dividend income	36,422		31,062		105,172		87,311
Interest Expense
Savings, NOW, and money market deposits	5,031		3,276		12,861		8,227
Time deposits	10,523		6,760		29,480		18,392
Repurchase agreements	517		390		1,511		897
Other short-term borrowings	2,289		1,135		5,702		2,920
Junior subordinated debentures	617		617		1,850		1,831
Notes payable	146		35		244		85
Total interest expense	19,123		12,213		51,648		32,352
Net interest income	17,299		18,849		53,524		54,959
Provision for loan losses	400		450		1,244		813
Net interest income after provision for loan losses	16,899		18,399		52,280		54,146
Noninterest Income
Trust income	1,707		1,580		5,494		4,858
Service charges on deposits	2,146		2,194		6,149		6,103
Gain on sale of loans	849		1,531		2,755		4,359
Secondary mortgage fees	201		288		513		759
Mortgage servicing income	133		62		348		112
Securities gains (losses), net	—		—		418		(5		)
Bank owned life insurance	483		218		1,444		652
Other income	1,355		1,501		4,193		4,113
Total noninterest income	6,874		7,374		21,314		20,951
Noninterest Expense
Salaries and employee benefits	9,193		8,780		27,293		26,880
Loss on settlement of benefit obligation	1,001		—		1,358		—
Occupancy expense, net	1,179		1,015		3,369		2,609
Furniture and equipment expense	1,418		1,378		3,958		3,827
Amortization of core deposit intangible assets	89		88		266		266
Advertising expense	485		473		1,461		1,311
Other expense	3,812		3,316		11,267		10,566
Total noninterest expense	17,177		15,050		48,972		45,459
Income before income taxes	6,596		10,723		24,622		29,638
Provision for income taxes	1,648		3,541		7,203		9,697
Net income	$	4,948	$	7,182	$	17,419	$	19,941

Basic earnings per share	$	0.37	$	0.53	$	1.30	$	1.48
Diluted earnings per share	$	0.37	$	0.52	$	1.28	$	1.46

ANALYSIS OF AVERAGE BALANCES,
TAX EQUIVALENT INTEREST AND RATES
Nine Months Ended September 30, 2006 and 2005
(Dollar amounts in thousands- unaudited)

	2006							2005
	Average							Average
	Balance			Interest		Rate		Balance			Interest		Rate
Assets
Interest bearing deposits with banks	$	531		$	3	0.76	%	$	443		$	2	0.60	%
Federal funds sold	143			5		4.66		289			7		3.23
Securities:
Taxable	322,589			9,518		3.93		335,522			8,785		3.49
Non-taxable (tax equivalent)	140,600			5,768		5.47		138,355			5,534		5.33
Total securities	463,189			15,286		4.40		473,877			14,319		4.03
Loans and loans held for sale	1,749,005			92,067		7.04		1,610,212			75,074		6.23
Total interest earning assets	2,212,868			107,361		6.49		2,084,821			89,402		5.73
Cash and due from banks	52,231			—		—		55,330			—		—
Allowance for loan losses	(15,984		)	—		—		(15,582		)	—		—
Other noninterest-bearing assets	120,950			—		—		88,306			—		—
Total assets	$	2,370,065						$	2,212,875

Liabilities and Stockholders’ Equity
Interest bearing transaction accounts	$	662,286		12,424		2.51		$	680,925		7,835		1.54
Savings accounts	117,697			437		0.50		125,188			392		0.42
Time deposits	944,317			29,480		4.17		804,390			18,392		3.06
Interest bearing deposits	1,724,300			42,341		3.28		1,610,503			26,619		2.21
Repurchase agreements	47,500			1,511		4.25		45,919			897		2.61
Other short-term borrowings	138,433			5,702		5.51		112,116			2,920		3.48
Junior subordinated debentures	31,625			1,850		7.80		31,625			1,831		7.72
Notes payable	5,427			244		6.01		2,812			85		4.04
Total interest bearing liabilities	1,947,285			51,648		3.55		1,802,975			32,352		2.40
Noninterest bearing deposits	253,570			—		—		251,682			—		—
Accrued interest and other liabilities	15,064			—		—		15,433			—		—
Stockholders’ equity	154,146			—		—		142,785			—		—
Total liabilities and stockholders’ equity	$	2,370,065						$	2,212,875
Net interest income (tax equivalent)				$	55,713						$	57,050
Net interest income (tax equivalent) to total earning assets						3.37	%						3.66	%
Interest bearing liabilities to earnings assets	88.00		%					86.48		%

Notes: Nonaccrual loans are included in the above stated average balances. Tax equivalent basis is calculated using a marginal tax rate of 35%.

The following tables provide a reconciliation of each non-GAAP measure to the most comparable GAAP equivalent. (Dollar amounts in thousands- unaudited)

	Three Months Ended						Year to Date
	September 30,						September 30,
	2006			2005			2006			2005
Net Interest Margin
Interest income (GAAP)	$	36,422		$	31,062		$	105,172		$	87,311
Taxable-equivalent adjustment:
Loans	57			57			170			154
Investments	677			681			2,019			1,937
Interest income—FTE	37,156			31,800			107,361			89,402
Interest expense (GAAP)	19,123			12,213			51,648			32,352
Net interest income—FTE	$	18,033		$	19,587		$	55,713		$	57,050
Net interest income—(GAAP)	$	17,299		$	18,849		$	53,524		$	54,959
Average interest earning assets	$	2,225,966		$	2,144,970		$	2,212,868		$	2,084,821
Net interest margin (GAAP)	3.08		%	3.49		%	3.23		%	3.52		%
Net interest margin—FTE	3.21		%	3.62		%	3.37		%	3.66		%

Efficiency Ratio
Noninterest expense	$	17,177		$	15,050		$	48,972		$	45,459
Noninterest income	6,874			7,374			21,314			20,951
Net interest income (GAAP)	17,299			18,849			53,524			54,959
Taxable-equivalent adjustment:
Loans	57			57			170			154
Investments	677			681			2,019			1,937
Net interest income—FTE	$	18,033		$	19,587		$	55,713		$	57,050
Noninterest income plus net interest income—FTE	$	24,907		$	26,961		$	77,027		$	78,001
Efficiency ratio	68.96		%	55.82		%	63.58		%	58.28		%