Mary Stuart, Countess of Bute and 1st Baroness Mount Stuart (February 1718-6 November 1794) was the daughter of Edward Wortley-Montagu and Lady Mary Pierrepont (the daughter of the 1st Duke of Kingston-upon-Hull).
On 27 August 1736, she married the future Prime Minister of the United Kingdom, John Stuart, 3rd Earl of Bute and had at least nine children by him:
- Lady Mary Stuart (c. 1741-5 April 1824), who married James Lowther, later the 1st Earl of Lonsdale, on 7 September 1761.
- John Stuart, 1st Marquess of Bute (30 June 1744 - 16 November 1814)
- Lady Anne Stuart (born c. 1745), who married Lord Warkworth, later the 2nd Duke of Northumberland, on 2 July 1764.
- The Hon. James Archibald Stuart (19 September 1747 - 1 March 1818)
- Lady Jane Stuart (c. 1748 - 28 February 1828), who married George Macartney, later the 1st Earl Macartney, on 1 February 1768.
- The Hon. Sir Charles Stuart (January 1753 - 25 May 1801)
- The Most Rev. and Hon. William Stuart, Archbishop of Armagh (Church of Ireland) (March 1755 - 6 March 1822)
- Lady Caroline Stuart (before 1763-20 January 1813), who married The Hon. John Dawson, later the 1st Earl of Portarlington, on 1 January 1778.
- Lady Louisa Stuart (12 August 1757 - 4 August 1851) Miller, Karl, Stuart, Lady Louisa (1757–1851), writer in Oxford Dictionary of National Biography, Oxford University Press, September 2004 & blank">online edition, January 2006 (subscription required) accessed 2 March 2008
In 1761, she was created Baroness Mount Stuart of Wortley, co. York and upon her death, was succeeded by her son, the _4th Earl of Bute.
In 1774, Mary Delany wrote to her friend Bernard Granville:
