Mary Stewart, Viscountess Mountjoy (1654–1720), formerly the Honourable Mary Coote, was the wife of William Stewart, 1st Viscount Mountjoy. She was the daughter of Richard Coote, 1st Baron Coote (1620-1683), and his wife, the former Mary St George.^[1] Her brother was Richard Coote, 1st Earl of Bellomont.

The viscount and viscountess had six sons and two daughters, including:^[2]

• Sir William Stewart, 2nd Viscount Mountjoy (1675–1728), who married Anne Boyle, daughter of Murrough Boyle, 1st Viscount Blesington, on 23 November 1696.^[2]
• Alexander Stewart, who had one daughter, Anne Stewart, his sole heiress.^[3]
• Mary Stewart (c. 1677–1765), who first married Archibald Preston (1672–1703). After his death, she married Vice Admiral George Forbes, 3rd Earl of Granard (1685–1765).
• Catherine Stewart, who married Arthur Davys (d. 1733), an Irish Member of Parliament, representing Carrickfergus in the Irish House of Commons.
• Charles Stewart (1681–1741), who became an officer in the Royal Navy and a Member of Parliament