William Shadrach Knox (September 10, 1843 – September 21, 1914) was an American lawyer and politician who served four terms as a U.S. Representative from Massachusetts who served from 1895 to 1903.

Born in Killingly, Connecticut, he moved with his parents to Lawrence, Massachusetts, in 1852; he attended the public schools and Amherst College where he studied the law.

In 1874 he became a member of the State house of representatives in 1874 and 1875, and he was city solicitor of Lawrence in 1875, 1876, and 1887-1890.

There he served as chairman, in the Committee on Territories (Fifty-fifth through Fifty-seventh Congresses).

He died in Lawrence, Massachusetts in 1914 and was interred in Bellevue Cemetery.