11-K

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 11–K

þ ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended December 31, 2010

OR

o TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from                      to                     

Commission file number 001-14423 [Plexus Corp.]

A. Full title of the plan and the address of the plan, if different from that of the issuer named below:

PLEXUS CORP. 401(k) SAVINGS PLAN

B. Name of issuer of the securities held pursuant to the plan and the address of its principal executive office:

PLEXUS CORP.
ONE PLEXUS WAY
NEENAH, WI 54956

Plexus Corp.
401(k) Savings Plan
Financial Statements and Supplemental Schedule
December 31, 2010 and 2009

Plexus Corp.
401(k) Savings Plan
Index to Financial Statements

	Page(s)
Report of Independent Registered Public Accounting Firm		1
Financial Statements
Statements of Net Assets Available for Benefits		2
Statement of Changes in Net Assets Available for Benefits		3
Notes to Financial Statements		4-12
Supplemental Schedule
Schedule H, Line 4i: Schedule of Assets (Held at End of Year)		13

Note:	Other schedules required by Section 2520.103-10 of the Department of Labor’s Rules and Regulations for Reporting and Disclosure under the Employee Retirement Income Security Act of 1974 have been omitted because they are not applicable.
EX-23.1

Report of Independent Registered Public Accounting Firm

Plan Administrator
Plexus Corp. 401(k) Savings Plan
Neenah, Wisconsin

We have audited the accompanying statements of net assets available for benefits of Plexus Corp. 401(k) Savings Plan as of December 31, 2010 and 2009, and the related statement of changes in net assets available for benefits for the year ended December 31, 2010. These financial statements are the responsibility of the Plan’s management. Our responsibility is to express an opinion on these financial statements based on our audits.

We conducted our audits in accordance with standards of the Public Company Accounting Oversight Board (United States). Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement. We were not engaged to perform an audit of the Plan’s internal control over financial reporting. Our audit included consideration of internal control over financial reporting as a basis for designing audit procedures that are appropriate in the circumstances, but not for the purpose of expressing an opinion on the effectiveness of the Plan’s internal control over financial reporting. Accordingly, we express no such opinion. An audit includes examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements. An audit also includes assessing the accounting principles used and significant estimates made by management, as well as evaluating the overall financial statement presentation. We believe that our audits provide a reasonable basis for our opinion.

In our opinion, the financial statements referred to above present fairly, in all material respects, the net assets available for benefits of Plexus Corp. 401(k) Savings Plan as of December 31, 2010 and 2009, and the changes in net assets available for benefits for the year ended December 31, 2010, in conformity with accounting principles generally accepted in the United States.

Our audits were performed for the purpose of forming an opinion on the basic financial statements taken as a whole. The supplemental schedule of assets (held at end of year) as of December 31, 2010, is presented for the purpose of additional analysis and is not a required part of the basic financial statements, but is supplementary information required by the Department of Labor’s Rules and Regulations for Reporting and Disclosure under the Employee Retirement Income Security Act of 1974. The supplemental schedule has been subjected to the auditing procedures applied in the audits of the basic financial statements and, in our opinion, is fairly stated in all material respects in relation to the basic financial statements taken as a whole.

Wipfli LLP

June 22, 2011
Green Bay, Wisconsin

1

Plexus Corp. 401(k) Savings Plan

Statements of Net Assets Available for Benefits
December 31, 2010 and 2009

	2010			2009
Assets
Investments, at fair value (See Notes 3 and 4)	$	168,612,673		$	140,086,770
Receivables
Employer’s contribution		20,489			14,608
Participants’ contributions		28,518			21,425
Notes receivable from participants		3,459,198			2,647,071
Total receivables		3,508,205			2,683,104
Total assets		172,120,878			142,769,874
Liabilities
Excess contributions payable to participants		—			138,622
Net assets reflecting investments at fair value		172,120,878			142,631,252
Adjustment from fair value to contract value for fully benefit-responsive investment contracts		(306,124	)		(29,030	)
Net assets available for benefits	$	171,814,754		$	142,602,222

The accompanying notes are an integral part of these financial statements.

2

Plexus Corp. 401(k) Savings Plan

Statement of Changes in Net Assets Available for Benefits
Year Ended December 31, 2010

Additions
Additions to net assets attributed to:
Investment income
Net appreciation in fair value of investments	$	18,351,480
Dividends		1,943,016
Total investment income		20,294,496
Interest income on notes receivable from participants		160,038
Contributions
Employer’s		5,781,160
Participants’		11,794,452
Total contributions		17,575,612
Total additions		38,030,146
Deductions
Deductions from net assets attributed to:
Benefits paid to participants		8,671,281
Administrative expenses		146,333
Total deductions		8,817,614
Net increase		29,212,532
Net assets available for benefits
Beginning of year		142,602,222
End of year	$	171,814,754

The accompanying notes are an integral part of these financial statements.

3

Plexus Corp. 401(k) Savings Plan

Notes to Financial Statements
December 31, 2010 and 2009

1. Description of Plan

The following description of the Plexus Corp. 401(k) Savings Plan (the “Plan”) provides only general information. Participants should refer to the Summary Plan Description (“SPD”) for a more complete description of the Plan’s provisions.

General

The Plan is a contributory defined contribution plan covering substantially all U.S. employees of Plexus Corp. (“Plexus,” the “Company” or the “Employer”) and affiliated employers, as defined. Employees are allowed to participate the first day of the month coinciding with or following their date of hire. The Plan is subject to the provisions of the Employee Retirement Income Security Act of 1974 (“ERISA”), as amended.

Contributions

Employee contributions are based on voluntary elections via phone or Internet by the participants, directing the Company to defer a stated amount from the participant’s compensation. Prior to January 1, 2010, participants could elect to defer up to 50% of their annual compensation. This limit increased to 75% as of January 1, 2010. New hires and rehires on and after January 1, 2007, are subject to automatic enrollment provisions under the Plan. Unless the new hire/rehire waives enrollment, employees were enrolled with a 2.5% deferral election prior to January 1, 2010. As of January 1, 2010, the percentage increased to 3%.

Prior to January 1, 2010, on a per pay period basis, the Company made a matching contribution on behalf of a participant equal to 100% of the first 2.5% of the participant’s compensation contributed to the Plan. Participants were eligible for the matching contribution the first day of the Plan year quarter coinciding with or following the date in which Plan eligibility requirements were met. As of January 1, 2010, the Company matching contribution increased to 100% of the first 4% of the participant’s compensation contributed to the Plan. In addition, as of January 1, 2010, participants are eligible for the matching contribution immediately following their date of hire. Contributions are limited by Section 401(k) of the Internal Revenue Code (the “IRC”). The Plan permits rollover contributions from other qualified plans; however, rollover contributions are not eligible for the Company matching contribution.

Investment Alternatives

Plan participants may direct their entire account balances in partial percentage increments to any of the various investment options offered by the Plan. Company contributions are also invested based upon participant allocation elections. Participants may change their investment options on a daily basis.

Participant Accounts and Allocations

Participant recordkeeping is performed by The Hartford Financial Services Group, Inc. (“Hartford”). For all investment programs which are mutual funds, Hartford maintains participant balances on a share method. Participant investments in the Plexus Unitized Stock Fund, Fixed Fund and Wells Fargo Stable Value-M Fund are accounted for on a unit value method. Units and unit values for these funds as of December 31, 2010 and 2009 were as follows:

4

Plexus Corp. 401(k) Savings Plan
Notes to Financial Statements
December 31, 2010 and 2009

	Units				Unit Value
	December 31,				December 31,
	2010		2009		2010		2009
Plexus Unitized Stock Fund		2,079,889		2,220,869	$	11.86	$	10.96
Fixed Fund		2,305		0		1.00		—
Wells Farge Stable Value-M Fund		305,214		326,400		45.59		44.47

Each participant’s account is credited with the participant’s contributions and allocations of Company contributions and Plan earnings (losses). Allocations of Plan earnings (losses) are based on participant account balances in relation to total fund account balances, as defined by the Plan document.

Vesting and Distributions

Participants immediately vest in all contributions made to the Plan. Participant accounts are distributable in the form of a lump sum payment or substantially equal installments of cash or in whole shares of Company securities as elected by the participant upon retirement, termination of employment, death, disability, financial hardship, or attainment of age 59-1/2. Participant account balances less than $1,000 may be automatically distributed in a lump sum. In addition, participant accounts can be rolled over into an individual retirement account (“IRA”) or another qualified defined contribution plan. Participant distributions may not be deferred past April 1 of the calendar year following the year in which the participant attains age 70-1/2. Forfeitures of unclaimed distributions are used to reduce Company matching contributions.

Notes Receivable from Participants

Participants may borrow from their accounts a minimum of $1,000 up to a maximum amount equal to the lesser of $50,000 or 50% of their vested account balance. Loan terms range up to five years. Loans are collateralized by the balance in the participant’s account and bear interest at the prime rate plus 1% at the time of loan origination. Principal and interest is paid ratably through regular payroll deductions.

Plan Reimbursement Account

As part of the recordkeeping and administrative service fee arrangement with Hartford, Hartford agrees to reimburse investment fund related revenue received by Hartford relating to the Plan that is in excess of the agreed upon service fee structure. The reimbursement amounts, if any, are paid to the Plan in a Plan Reimbursement Account. Investment fund related revenue received by Hartford typically includes Rule 12b-1 fees and service fees paid by the fund or the fund’s affiliates. The Plan Reimbursement Account may be used by the Plan to pay direct and necessary expenses of the Plan; these fees are reflected as appreciation in investments.

2. Summary of Significant Accounting Policies

Accounting Method

The financial statements of the Plan are prepared under the accrual method of accounting.

As described in the accounting guidance issued by the Financial Accounting Standards Board, investment contracts held by a defined contribution plan are required to be reported at fair value. However, contract value is the relevant measurement attribute for that portion of the net assets

5

Plexus Corp. 401(k) Savings Plan
Notes to Financial Statements
December 31, 2010 and 2009

available for benefits of a defined contribution plan attributable to fully benefit-responsive investment contracts because contract value is the amount participants would receive if they were to initiate permitted transactions under the terms of the Plan. As required by the accounting guidance, the Statements of Net Assets Available for Benefits presents the fair value of the investment contracts as well as the adjustment of the fully benefit-responsive investment contracts from fair value to contract value. The Statement of Changes in Net Assets Available for Benefits is prepared on a contract value basis.

Use of Estimates

The preparation of the accompanying financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, and changes therein, and disclosure of contingent assets and liabilities. Actual results could differ from those estimates.

Investment Valuation and Income (Loss) Recognition

The Plan’s investments are stated at fair value. Fair value is the price that would be received on the sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. See Note 4 for a discussion of fair value measurements.

The Plan presents in the Statement of Changes in Net Assets Available for Benefits, the net appreciation (depreciation) in the fair value of its investments which consists of the realized gains or losses and the unrealized appreciation (depreciation) on those investments. Purchases and sales of investments are recorded on a trade-date basis. Dividends are recorded on the ex-dividend date. Interest is recognized when earned.

Notes Receivable from Participants

Notes receivable from participants are measured at their unpaid principal balance plus any accrued but unpaid interest. Delinquent participant loans are reclassified as distributions based upon terms of the Plan document.

Risks and Uncertainties

The Plan provides for various investment options in a combination of different investment securities. The Plan’s investments are exposed to various risks, such as interest rate, market, and credit risks. Due to the level of risk associated with certain investments and the level of uncertainty related to changes in the values of investments, it is at least reasonably possible that changes in risks in the near term would materially affect participants’ account balances and the amounts reported in the Statements of Net Assets Available for Benefits and the Statement of Changes in Net Assets Available for Benefits.

Payment of Benefits

Benefits are recorded when paid except for any excess contributions payable to participants, which are recorded as they become payable.

Administrative Expenses

Certain expenses incurred in the administration of the Plan are paid by the Company and are not reflected within these financial statements.

6

Plexus Corp. 401(k) Savings Plan
Notes to Financial Statements
December 31, 2010 and 2009

New Accounting Pronouncements

During 2010, the Plan adopted Accounting Standards Update (ASU) 2010-25, Reporting Loans to Participants by Defined Contribution Pension Plans. ASU 2010-25 requires defined contribution plans to classify loans to participants as notes receivable from participants. The classification of participant loans as notes receivable acknowledges that participant loans are unique from other investments, and measuring participant loans at their unpaid principal balance plus any accrued but unpaid interest is more meaningful to users of financial statements rather than measuring participant loans at fair value. A reclassification of the 2009 participant loans from investments to notes receivable from participants was made due to the adoption of ASU 2010-25.

Subsequent Events

Subsequent events have been evaluated through the date the financial statements were issued.

7

Plexus Corp. 401(k) Savings Plan
Notes to Financial Statements
December 31, 2010 and 2009

3. Investments

The following presents investments that represent 5% or more of the Plan’s net assets:

	2010		2009
Plexus Unitized Stock Fund, 2,079,889 and 2,220,869 units, respectively	$	24,663,737	$	24,348,274
Vanguard Institutional Index Fund, 182,676 and 174,352 shares, respectively		21,009,558		17,780,389
Columbia Small Cap Growth II Fund, 1,430,120 and 1,431,146 shares, respectively		17,347,360		13,567,264
American EuroPacific Growth Fund, 417,462 and 428,607 shares, respectively		17,270,414		16,432,804
Wells Fargo Stable Value-M Fund*, 305,214 and 326,400 shares, respectively		13,914,723		14,515,006
Vanguard Total Bond Market Index Fund, 1,123,505 and 772,392 shares, respectively		11,909,151		7,994,262
American Beacon Large Cap Fund, 626,373 and 602,634 shares, respectively		11,606,692		9,895,251
T. Rowe Price Intl. Growth and Income Fund, 651,452 and 458,479 shares, respectively		8,716,435		*	*

*	Investment contract shown at contract value, which is the relevant measurement attribute for fully benefit-responsive investment contracts.
**	Represents less than 5% of the Plan’s net assets for this year.

During 2010, the Plan’s investments (including gains and losses on investments bought and sold, as well as held during the year) appreciated in value by $18,351,480, as follows:

Mutual Funds	$	15,356,437
Common Stock		2,647,657
Collective/Common Trust Funds		347,386
	$	18,351,480

4. Fair Value Measurements

Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (i.e., the exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The accounting standards establish a fair value hierarchy based on three levels of inputs that may be used to measure fair value.

8

Plexus Corp. 401(k) Savings Plan
Notes to Financial Statements
December 31, 2010 and 2009

The input levels are:

Level 1: Quoted (observable) market prices in active markets for identical assets or liabilities.

Level 2: Inputs other than Level 1 that are observable, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the asset or liability.

Level 3: Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the asset or liability.

The asset’s or liability’s fair value measurement level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Valuation techniques used need to maximize the use of observable inputs and minimize the use of unobservable inputs.

The following is a description of the valuation methodologies used for assets measured at fair value:

Mutual funds: Valued at the net asset value (NAV) of shares held by the Plan at year end. The NAV is a quoted price in an active market.

Common stock: Valued at the closing price reported on the active market on which the individual securities are traded.

Collective/Common trust funds: Valued at the net asset value (NAV) of shares held by the Plan at year end. The NAV’s share price is quoted on a private market that is not active; however, the unit price is based on underlying investments which are traded on an active market.

The preceding methods described may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. Furthermore, although the Plan believes its valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date.

9

Plexus Corp. 401(k) Savings Plan
Notes to Financial Statements
December 31, 2010 and 2009

     The following table lists the fair values of investments as of December 31, 2010:

	Fair Value Measurements Using Input Levels:
	Level 1		Level 2		Level 3		Total
Mutual funds
Growth funds	$	47,995,743	$	—	$	—	$	47,995,743
Index funds		32,918,709		—		—		32,918,709
Value funds		15,375,492		—		—		15,375,492
Other funds		33,435,840		—		—		33,435,840
Total mutual funds		129,725,784		—		—		129,725,784
Common stock		24,663,737		—		—		24,663,737
Collective / Common trust funds		—		14,223,152		—		14,223,152
Total investments measured at fair value	$	154,389,521	$	14,223,152	$	—	$	168,612,673

     The following table lists the fair values of investments as of December 31, 2009:

	Fair Value Measurements Using Input Levels:
	Level 1		Level 2		Level 3		Total
Mutual funds
Growth funds	$	40,523,019	$	—	$	—	$	40,523,019
Index funds		25,774,651		—		—		25,774,651
Value funds		12,204,153		—		—		12,204,153
Other funds		22,692,637		—		—		22,692,637
Total mutual funds		101,194,460		—		—		101,194,460
Common stock		24,348,274		—		—		24,348,274
Collective / Common trust funds		—		14,544,036		—		14,544,036
Total investments measured at fair value	$	125,542,734	$	14,544,036	$	—	$	140,086,770

10

Plexus Corp. 401(k) Savings Plan
Notes to Financial Statements
December 31, 2010 and 2009

5. Net Asset Value Per Share

The following table sets forth additional disclosures of the Plan’s investments whose fair value is estimated using net asset value per share (or its equivalent) as of December 31, 2010 and 2009:

	Fair Value Estimated Using Net Asset Value per Share
	December 31, 2010
					Other	Redemption
			Unfunded	Redemption	Redemption	Notice
Investment	Fair Value*		Commitment	Frequency	Restrictions	Period
Wells Fargo Stable
Value-M Fund**	$	14,220,847	none	Daily	none	none

	Fair Value Estimated Using Net Asset Value per Share
	December 31, 2009
					Other	Redemption
			Unfunded	Redemption	Redemption	Notice
Investment	Fair Value*		Commitment	Frequency	Restrictions	Period
Wells Fargo Stable
Value-M Fund**	$	14,544,036	none	Daily	none	none

*	The fair value of the investment has been estimated using the net asset value of the investment.
**	Investments are in general insurance contracts and security-backed contracts in which each contract issuer specifies specific events which may trigger a market value adjustment. At this time, the investment fund does not believe that the occurrence of any such market value event, which would limit the investment fund’s ability to transact at contract value with participants, is probable.

6. Amounts Allocated to Withdrawn Participants

Approximately $32,300,000 and $29,095,000 of Plan assets have been allocated to the accounts of persons who are no longer active participants of the Plan as of December 31, 2010 and 2009, respectively, but who have not yet received distributions as of that date.

7. Tax Status

The Internal Revenue Service has determined and informed the Company by a letter dated November 8, 2004, that the Plan is designed in accordance with applicable sections of the IRC. Although the Plan has been amended since receiving the determination letter, the Plan’s administrator and the Plan’s tax counsel believe that the Plan is designed and is currently being operated in compliance with the applicable requirements of the IRC. Therefore, no provision for income taxes has been included in the Plan’s financial statements.

GAAP requires Plan management to evaluate tax positions taken by the Plan and recognize a tax liability (or asset) if the Plan has taken an uncertain position that more likely than not would not be

11

Plexus Corp. 401(k) Savings Plan
Notes to Financial Statements
December 31, 2010 and 2009

sustained upon examination by the IRS. The Plan administrator has analyzed the tax positions taken by the Plan, and has concluded that as of December 31, 2010, there are no uncertain positions taken or expected to be taken that would require recognition of a liability (or asset) or disclosure in the financial statements. The Plan is subject to routine audits by taxing jurisdictions; however, there are currently no audits for any tax periods in progress. The Plan administrator believes it is no longer subject to income tax examinations for years prior to 2007.

8. Plan Termination

Although it has not expressed any intent to do so, the Company has the right under the Plan to discontinue its contributions at any time and to terminate the Plan subject to the provisions of ERISA.

9. Related-Party Transactions

Certain Plan investments represent Employer securities. Transactions involving these investments are considered party-in-interest transactions. These transactions are not, however, considered prohibited transactions under 29 CFR 408(b) of the ERISA regulations.

10. Reclassification

Certain amounts in the prior year’s financial statements have been reclassified to conform to the presentation of information for the year ended December 31, 2010.

12

Plexus Corp. 401(k) Savings Plan

EIN: 39-1344447, PN: 001

Schedule of Assets (Held at End of Year)
December 31, 2010

Identity of Issuer,
Borrower, Lessor	Description
or Similar Party	of Investment	Current Value **
* Plexus Unitized Stock Fund	Common Stock	$	24,663,737
Vanguard Institutional Index Fund	Mutual Fund		21,009,558
Columbia Small Cap Growth II Fund	Mutual Fund		17,347,360
American EuroPacific Growth Fund	Mutual Fund		17,270,414
Wells Fargo Stable Value-M Fund	Collective Trust Fund		13,914,723
Vanguard Total Bond Market Index Fund	Mutual Fund		11,909,151
American Beacon Large Cap Value Fund	Mutual Fund		11,606,692
T. Rowe Price Intl. Growth and Income Fund	Mutual Fund		8,716,435
T. Rowe Price Real Estate Fund	Mutual Fund		8,076,225
Lazard Emerging Markets Inst Fund	Mutual Fund		7,935,762
MFS Aggressive Growth Allocation Fund	Mutual Fund		6,054,656
T. Rowe Price Blue Chip Growth Fund	Mutual Fund		5,204,692
MFS Conservative Allocation Fund	Mutual Fund		5,019,098
Columbia Small Cap Value I Fund	Mutual Fund		3,768,800
MFS Moderate Allocation Fund	Mutual Fund		3,688,320
MFS Growth Allocation Fund	Mutual Fund		2,118,621
Fixed Fund	Common Trust Fund		2,305
		$	168,306,549
* Participant Loans	Interest rates ranging from 4.25% to 9.25%; maturity dates ranging from 2011 to 2015	$	3,459,198

*	Party-in-interest.
**	Related cost information is not required for participant-directed investments.

13

SIGNATURES

     The Plan. Pursuant to the requirements of the Securities Exchange Act of 1934, the trustees (or other persons who administer the employee benefit plan) have duly caused this annual report to be signed on its behalf by the undersigned hereunto duly authorized.

	PLEXUS CORP. 401(k) SAVINGS PLAN
Date: June 22, 2011
	/s/ Angelo M. Ninivaggi
	Angelo M. Ninivaggi
	Senior VP, General Counsel, Corporate Compliance Officer & Secretary of Plexus Corp.

14

EX-23.1

Exhibit 23.1

Consent of Independent Auditors

We hereby consent to the incorporation by reference in the Registration Statement on Form S-8 (File No. 333-76728) of Plexus Corp. of our report dated June 22, 2011 relating to the financial statements and schedule of Plexus Corp. 401(k) Savings Plan, which appears in this Annual Report (Form 11-K) for the year ended December 31, 2010.

Wipfli LLP

June 22, 2011
Green Bay, Wisconsin