William Allen ( December 27, 1803 – July 11, 1879) was a Democratic Representative and Senator from Ohio and Governor of Ohio.

Allen was born in Edenton, North Carolina. His sister, Mary Granberry Allen, married Pleasant Thurman, and their son, Allen G. Thurman, followed in his uncle's footsteps, becoming a lawyer and politician. Allen moved to Chillicothe, Ohio in 1819 and he and his sister lived there together.

He served as a Representative from Ohio from 1832 to 1834, when he lost a bid for re-election, and Senator from Ohio from 1837 to 1849, losing a bid for re-election in 1848. Allen then retired to his farm, "Fruit Hill," near Chillicothe, Ohio, and did not return to public service for nearly a quarter century. He served as Governor of Ohio from 1874 to 1876. He unsuccessfully sought a second two-year term in an 1875 election.