The Stewart family of Stewart's Court and Ballylawn, near Moville, in Co. Donegal were settled there by the early 17th century. In 1744 Alexander Stewart employed a portion of his wife's legacy from her brother, Sir Robert Cowan, to purchase the manors of Newtown and Comber, Co. Down; she had also inherited a small estate in Co. Londonderry and some property in Londonderry City. Their son, Robert, 1st Marquess of Londonderry, expanded the properties and enlarged Mount Stewart 1803-5. The 3rd Marquess had a successful miltiary and political career, married the heiress to the Vane-Tempest Co. Durham estates and collieries and built a thriving seaport at Seaham. His brother, Lord Castlereagh, was Secretary of State and a very astute statesman. Mount Stewart was acquired by the National Trust in 1955; at the start of the 21st century a descendant, Lady Mairi Bury, lives there.