FORM OF VOTING AGREEMENT

EXHIBIT 99.1

EXHIBIT A

FORM OF VOTING AGREEMENT

     This Voting Agreement (this “ Agreement ”) is made and entered into as of December 16, 2007, by and among S&T Bancorp, Inc., a Pennsylvania corporation, (“ Purchaser ”), and each of the individual, natural persons identified on Schedule A hereto (individually a “ Shareholder ” and collectively the “ Shareholders ”).

     WHEREAS, concurrently with the execution of this Agreement, IBT Bancorp, Inc., a Pennsylvania corporation (“ Seller ” or the “ Company ”) and Purchaser have entered into an Agreement and Plan of Merger (the “ Merger Agreement ”) that provides for the merger (the “ Merger ”) of Seller with and into Purchaser pursuant to the terms thereof;

     WHEREAS, as an essential condition and inducement to Purchaser to enter into the Merger Agreement and in consideration therefor, the Shareholders and Purchaser have agreed to enter into this Agreement;

     WHEREAS, as of the date hereof, the Shareholders are the record holders and beneficial owners of the shares of common stock, par value $1.25 per share, of the Company (the “ Shares ”) set forth on Schedule A hereto (which do not include shares held in a fiduciary capacity or options) and desire to enter into this Agreement with respect to such Shares (for purposes of this Agreement, “beneficial ownership” shall have the meaning given to such term in Rule 13d-3 under the Securities Exchange Act of 1934, as amended (the “ Exchange Act ”)); and

     WHEREAS, Purchaser desires the Shareholders to agree, and the Shareholders are willing to agree, (i) not to transfer or otherwise dispose of any of the Shares prior to the Expiration Date (as defined in Section 1.1 below) and (ii) to vote the Shares so as to facilitate consummation of the Merger.

     NOW, THEREFORE, in consideration of the foregoing and the mutual covenants and agreements contained herein and in the Merger Agreement, and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, and intending to be legally bound hereby, the parties hereto hereby agree as follows:

     1.  Agreement to Retain and Vote Shares .

          1.1 Transfer and Encumbrance . The Shareholders agree not to transfer (except as may be specifically required by court order), sell, exchange, pledge or otherwise dispose of or encumber any of the Shares or to make any offer or agreement relating thereto other than in accordance with the Merger, at any time prior to the Expiration Date. As used herein, the term “ Expiration Date ” shall mean the earlier to occur of: (a) such date and time as the Merger shall become effective in accordance with the terms and provisions of the Merger Agreement and (b) such date as the Merger Agreement is terminated pursuant to the terms and provisions thereof, including, without limitation, in accordance with Section 8.01 thereof.

          1.2 Agreement to Vote Shares . From the date hereof until the Expiration Date, at every meeting of the shareholders of the Company, and at every adjournment or postponement thereof, and on every action or approval by written consent of the shareholders of the Company, the Shareholders shall, including by written consent if requested by Purchaser, vote (or cause to be voted) the Shares (i) in favor of adoption and approval of the Merger Agreement, the Merger and any matter that could reasonably be expected to facilitate the Merger and (ii) against any amendment of the Company’s articles of incorporation or bylaws or other proposal, transaction, agreement or acquisition proposal involving the Company or any of its subsidiaries which amendment or other proposal or transaction would in any manner impede, frustrate, prevent or nullify, or result in a breach of any covenant, representation or warranty or any other obligation or agreement of the Company under or with respect to, the Merger, the Merger Agreement or any of the other transactions contemplated by the Merger Agreement. The Shareholders agree not to take any actions contrary to the Shareholders’ obligations under this Agreement.

          1.3 Revocation of Other Proxies . To the extent inconsistent with the other provisions of this Agreement or the Merger Agreement, the Shareholders hereby revoke any and all previous proxies with respect to the Shareholders’ Shares.

          1.4 Representations, Warranties and Covenants of the Shareholders . Each Shareholder hereby represents, warrants and covenants to Purchaser as follows:

               (a)  Ownership of Shares; Authority . The Shareholder (i) is the record and beneficial owner of the Shares, which at the date hereof and at all times up until the Expiration Date will be free and clear of any liens, claims, options, charges or other encumbrances; (ii) has full power and authority to make, enter into and carry out the terms of this Agreement; and (iii) is not a party to any voting trusts, proxies or any other agreements or understandings with respect to the voting of the Shares.

               (b)  No Conflicts or Consents . The execution and delivery of this Agreement by the Shareholder does not, and the performance by the Shareholder of the Shareholder’s obligations under this Agreement will not: (i) conflict with or violate any law, rule, regulation, order, decree or judgment applicable to the Shareholder or by which its properties