William Crichton-Dalrymple, 5th Earl of Dumfries, 4th Earl of Stair, KT (1699 – 27 July 1768) was a Scottish peer. He inherited the title of Earl of Dumfries in 1742, upon the death of his mother Penelope Crichton, 4th Countess of Dumfries. He also held the heritable position of the Sheriff of Clackmannan from 1742 until heritable sheriffdoms were abolished in 1747. He served in the Army from 1721 to 1747, and was aide-de-Camp to his uncle, John Dalrymple, 2nd Earl of Stair, at the Battle of Dettingen in 1743.