William Johnston (1819 – May 1, 1866) was an American lawyer and politician who served one term as a U.S. Representative from Ohio from 1863 to 1865.

Born on the island of Ireland (the entirety of which was then part of the U.K.) in 1819, Johnston immigrated to the United States and settled in Ohio.

He was admitted to the bar and practiced in Mansfield, Ohio, from 1859 to 1863.

He was an unsuccessful candidate for reelection in 1864 to the Thirty-ninth Congress.

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