William Allen (August 13, 1827 – July 6, 1881) was a United States Representative from Ohio during the early part of the American Civil War, serving two terms from 1859 to 1863.

Allen was born near Hamilton, Ohio, where he attended the public schools.

Allen was admitted to the bar in 1849 and commenced practice in Greenville, Ohio, in 1850.

He became affiliated with the Republican Party at the close of the Civil War and was appointed judge of the Court of Common Pleas of the second judicial district in 1865.

He declined the Republican nomination for election to the Forty-sixth Congress in 1878 because of failing health.