Exhibit 99.1

S&T Bancorp, Inc. Announces 2011 Results

Indiana, Pennsylvania – S&T Bancorp, Inc. (NASDAQ: STBA), a full-service financial institution with office locations in 10 Pennsylvania counties, has announced its full year and fourth quarter earnings for 2011.

Todd D. Brice, president and chief executive officer of S&T Bancorp, Inc., offered the following highlights:

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S&T Bancorp, Inc. Announces 2011 Results (continued)

“In 2011, S&T Bank had success in two areas that will generate plenty of momentum as we move into 2012,” said Todd D. Brice, president and chief executive officer. “First, we redeemed all of the preferred stock we issued through the U.S. Treasury’s Capital Purchase Program, a move that will boost earnings in 2012 by $0.22 per share. Second, we announced the pending acquisition of Mainline Bancorp, which is expected to close in the first quarter of 2012. This merger will capitalize on the synergies between our two banks and give us a greater presence in key regions that include Blair and Cambria counties.”

U.S Treasury’s Capital Purchase Program

During the fourth quarter, S&T redeemed all of the preferred stock it sold to the U.S. Department of the Treasury in January of 2009 as part of the CPP. S&T’s strong capital position allowed for the repurchase of the preferred shares without raising additional capital and without any conditions from regulators. S&T used available cash to fund the repurchase of the outstanding preferred stock for $108.7 million and the payment of the final dividend of $0.3 million. As a result of this redemption, a one-time non-cash reduction in net income available to common shareholders of approximately $1.8 million or $0.06 per common diluted share was recognized to accelerate the accretion of the discount for the preferred stock.

Net Interest Income (FTE)

Net interest income and net interest margin on a fully taxable equivalent basis decreased from the prior year primarily due to a shift in asset mix from loans to lower yielding securities. This shift in asset mix is a result of significant loan pay downs during 2011. Net interest income for the full year 2011 was $141.5 million compared to $150.5 million in 2010. The net interest margin declined in 2011 to 3.83% from 4.05% in 2010. Average loans decreased $169.2 million from the prior year, while the yield decreased by 21 basis points to 4.88%. The decrease in loans was offset by an increase in average securities of $153.0 million mainly due to an increase in excess funds held at the Federal Reserve.

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S&T Bancorp, Inc. Announces 2011 Results (continued)

These excess funds have decreased the yield on securities by 132 basis points to 2.58%.

Net interest income for the fourth quarter of 2011 was $35.2 million compared to $34.9 million in the third quarter of 2011. The net interest margin increased to 3.79% in the fourth quarter of 2011 compared to 3.76% in the third quarter of 2011. The increase in income and rate is due to favorable borrowing and certificate of deposit repricing, combined with higher loan related fees.

Asset Quality

Asset quality metrics continue to show improvement. Nonperforming assets decreased to $60.1 million or 1.92% of total loans plus OREO compared to $65.2 million or 2.08% in the third quarter of 2011 and down from $69.7 million or 2.07% in the fourth quarter of 2010. Included in nonperforming assets were troubled debt restructurings (TDRs) of $18.2 million. These restructured loans are a result of our continued efforts to work directly with our customers through the current challenging economic cycle.

The provision for loan losses decreased in 2011 to $15.6 million from $29.5 million in 2010. Net charge-offs were also down significantly in 2011, to 0.56% of average loans compared to 1.11% in 2010. For the fourth quarter of 2011, the provision for loan losses was $2.3 million compared to $1.5 million for the third quarter of 2011 and $7.7 million in the fourth quarter of 2010. Net charge-offs were $5.0 million for the fourth quarter compared to $8.0 million in the third quarter and $12.6 million in the fourth quarter of 2010. The decrease in provision during 2011 is primarily a result of a general improvement in asset quality.

The allowance for loan losses at December 31, 2011 was $48.8 million or 1.56% of total loans, as compared to $51.5 million or 1.64% at September 30, 2011 and $51.4 million or 1.53% at December 31, 2010. The allowance to nonperforming loans was 87% at both December 31, 2011 and September 30, 2011 and 80% at December 31, 2010. Included in the allowance is $5.5 million of specific reserves compared to $2.9 million in the third quarter of 2011 and $3.6 million in the fourth quarter of 2010.

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S&T Bancorp, Inc. Announces 2011 Results (continued)

Noninterest Income

Noninterest income decreased $2.7 million to $44.2 million for the full year 2011 compared to $46.9 for the full year 2010. The decrease from the prior year primarily relates to a $2.2 million decline in mortgage banking and a $1.2 million decline in service charges and fees on deposits. The decrease in mortgage banking is due to lower volume of loan sales in the secondary market. The decrease in service charges and fees relates to a $1.8 million decline in overdraft fees due to regulatory changes that took effect in August 2010. This decrease was partially offset by an increase in new deposit related fees of $0.5 million in 2011.

Noninterest income for the fourth quarter increased to $11.6 million compared to $10.4 million in the third quarter of 2011. The increase of $1.2 million primarily relates to mortgage banking activities. During the third quarter, lower interest rates resulted in a decrease in the value of the mortgage servicing rights asset of $0.8 million, and in the fourth quarter, increased activity resulted in an increase in fees of $0.2 million.

Noninterest Expense

Noninterest expense decreased for the full year 2011 by $1.7 million to $103.9 million compared to $105.6 million in 2010. The decrease was driven by a reduction of $1.9 million in FDIC expense as a result of a change in methodology for the assessment and a $1.1 million decrease in loan collection fees as asset quality improved. During 2010 there were one time costs of $2.3 million for a legal settlement and a $1.1 million write-off of start-up expenses for a mutual fund advised by an affiliate. These decreases were offset by higher salaries and benefits cost of $1.5 million primarily related to annual merit increases.

Noninterest expense for the fourth quarter was $26.7 million compared to $24.2 million for the third quarter of 2011. The increase from the third quarter of 2011 includes higher

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S&T Bancorp, Inc. Announces 2011 Results (continued)

salaries and benefits of $1.2 million primarily related to higher medical cost in the current quarter and increased incentive plan expense. Also, there was a reduction in the reserve for unfunded loan commitments of $1.2 million in the third quarter compared to a reduction of $0.5 million in the fourth quarter. The $0.5 million reduction in reserves in the fourth quarter is due to a decline in available commitments.

Financial Condition

Total assets have remained relatively unchanged since the fourth quarter of 2010 at $4.1 billion. The decline in loan balances has been offset by commensurate increases in securities, primarily excess cash held at the Federal Reserve. An encouraging sign is the significant slowdown in the decline of loan balances experienced in the fourth quarter of 2011. Gross loans decreased by only $3.5 million in the fourth quarter compared to a decrease of $227.8 million in the first three quarters of 2011. Deposits remained little changed at $3.3 billion since the fourth quarter of 2010, although with some improvement in mix.

S&T’s capital ratios declined due to the redemption of the CPP, but remain significantly above the “well capitalized” thresholds of federal bank regulatory agencies with a tier 1 leverage capital ratio of 9.17%, tier 1 risk-based capital ratio of 11.63% and total risk-based capital ratio of 15.20%. S&T’s tangible common equity ratio was 8.09% for the fourth quarter of 2011 compared to 8.30% for the third quarter of 2011 and 7.61% for the fourth quarter of 2010. The decline in the fourth quarter of 2011 is due to an increase in the pension liability caused by a lower discount rate.

About S&T Bancorp, Inc.

Headquartered in Indiana, PA, S&T Bancorp, Inc. operates offices within Allegheny, Armstrong, Blair, Butler, Cambria, Clarion, Clearfield, Indiana, Jefferson and Westmoreland counties. With assets of $4.1 billion, S&T Bancorp, Inc. stock trades on the NASDAQ Global Select Market System under the symbol STBA. For more information, visit www.stbancorp.com.

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S&T Bancorp, Inc. Announces 2011 Results (continued)

This information may contain forward-looking statements regarding future financial performance which are not historical facts and which involve risks and uncertainties. Actual results and performance could differ materially from those anticipated by these forward-looking statements. Factors that could cause such a difference include, but are not limited to, general economic conditions, change in interest rates, deposit flows, loan demand, asset quality, including real estate and other collateral values and competition. In addition to the results of operations presented in accordance with Generally Accepted Accounting Principles (GAAP), S&T management uses and this press release contains or references, certain non-GAAP financial measures, such as net interest income on a fully taxable equivalent basis. S&T believes these non-GAAP financial measures provide information useful to investors in understanding our underlying operational performance and our business and performance trends as they facilitate comparisons with the performance of others in the financial services industry. Although S&T believes that these non-GAAP financial measures enhance investors’ understanding of S&T’s business and performance, these non-GAAP financial measures should not be considered an alternative to GAAP. A reconciliation of these non-GAAP financial measures is presented in the attached financial data spreadsheet. This information should be read in conjunction with the audited financial statements and analysis as presented in the Annual Report on Form 10-K for S&T Bancorp, Inc. and subsidiaries.

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