Margaret Wemyss, 3rd Countess of Wemyss

Margaret Wemyss, 3rd Countess of Wemyss and Countess of Cromarty (1 January 165911 March 1705) was a Scottish peer.

Margaret was the daughter of David Wemyss, 2nd Earl of Wemyss and Margaret Leslie, daughter of John Leslie, 6th Earl of Rothes. She was the youngest of sixteen children; she and her older sister, Lady Jean Wemyss (a half-sister by her father's first wife), were the only ones who did not die young and childless. Lady Margaret (1 April 1677 – 29 March 1763), married David Carnegie, 4th Earl of Northesk. David, later 4th Earl of Wemyss (1678–1720).

After Lord Burntisland died in 1682, the Countess married Sir George Mackenzie of Tarbat (later created Earl of Cromartie).