Margaret Wemyss, 3rd Countess of Wemyss and Countess of Cromarty (1 January 1659 – 11 March 1705) was a Scottish peer in her own right.
Margaret was the daughter of David Wemyss, 2nd Earl of Wemyss and Margaret Leslie, daughter of John Leslie, 6th Earl of Rothes. She succeeded to the family title in 1679, as the only child to outlive her father.
On 28 March 1672, Margaret married her cousin, Sir James Weymss of Caskieberry (later created Lord Burntisland for life) and they had three surviving children:
Lady Anne (d. 1702), married David Melville, 3rd Earl of Leven
David, later 4th Earl of Wemyss (1678–1720)
Lady Margaret (?–?), married David Carnegie, 4th Earl of Northesk.
After Lord Burntisland died in 1682, the countess married Sir George Mackenzie of Tarbat (later created Earl of Cromartie).