Frank Trimble O'Hair (March 12, 1870 – August 3, 1932) was a U.S. Representative from Illinois.

O'Hair attended the common schools and was graduated from the law department of De Pauw University in Greencastle, Indiana, in 1893.

He was an unsuccessful candidate for reelection in 1914 to the Sixty-fourth Congress, losing to Cannon (who regained his seat).

This repeated the pattern of fellow Democratic banker Samuel T. Busey who took Cannon's seat for one congressional interval 22 years earlier.

This article incorporates public domain material from the Biographical Directory of the United States Congress