William Cox Ellis (5 May 1787-13 December 1871) was a member of the US House of Representatives (F-PA 9) from 4 March 1823 to 3 March 1825, succeeding John Brown. Born in Muncy, Pennsylvania, Ellis served as a bank cashier and as a lawyer in his hometown before serving in Congress. A Jacksonian Federalist, he later joined the Republican Party in 1856.