S&T Bancorp Inc. announced yesterday that it would acquire IBT Bancorp Inc., in a stock and cash deal worth about $171 million, to expand into Westmoreland and Allegheny counties.

The combined company will have more than $4.1 billion in assets and improve its market share to about 12 percent in Westmoreland County.

Under the terms of the merger agreement, which was unanimously approved by the boards of directors of both companies, S&T Bancorp will acquire all of the outstanding shares of IBT Bancorp for a total purchase price of about $171 million.

IBT shareholders can elect to receive $31 in cash per each share of their stock, S&T common stock, or a combination of both, with certain restrictions. The deal is expected to be a tax-free exchange for IBT shareholders who receive stock, S&T said.

The merger is expected to be completed in the second quarter of 2008.

Indiana, Pa.-based S&T has 46 offices and 700 employees, while Irwin-based IBT has nine branch offices and 225 employees. There was no word on whether all the jobs would be retained.

IBT shares yesterday shot up 45 percent, or $8.61, to $27.80, while S&T Bancorp closed at $28.63, down 22 cents.