Vane-Tempest-Stewart family, Marquesses of Londonderry

The Stewart family settled in the early 17th century in County Donegal, where Ballylawn became its seat. Alexander Stewart (1699-1781) married his cousin Mary, sister and heir of Sir Robert Cowan (d. 1738), through whom he inherited property in County Londonderry, and he also bought lands in County Down, acquiring the manors of Newtown and Comber in 1744. The County Down estates were extended by his son Robert (1739-1821), who built Mount Stewart, and who was created Baron Londonderry in 1789, Viscount Castlereagh in 1795, Earl of Londonderry in 1796 and Marquess of Londonderry in 1816.

The 2nd Marquess (1769-1822), known for most of his political career as Lord Castlereagh, married in 1794 Amelia (or Emily), daughter and co-heir of the 2nd Earl of Buckinghamshire (for the descent of her properties see Kerr, Marquesses of Lothian). He was succeeded by his brother Charles (1778-1854), who in 1819 had married Frances Anne, daughter of Sir Henry Vane-Tempest, 2nd Bt (1771-1813). She was heir through her father to the Vane and Tempest estates in County Durham (see below), and though her mother, Countess of Antrim in her own right, to Carnlough and other properties in County Antrim. The County Durham estates descended to her son Lord Vane (see below), but the County Antrim properties, following the death of her grandson Lord Herbert Vane-Tempest in 1921, to the family of her daughter Frances, Duchess of Marlborough.

The Tempest family was of medieval origin in County Durham, and enlarged its estates by marriages with the Heath and Wharton families in 1642 and 1706 respectively. John Tempest (1710-76) purchased Wynyard and other estates, but his son John died without surviving issue in 1794, leaving his estates to his nephew Sir Henry Vane, later Vane-Tempest, 2nd Bt, son of Sir Henry Vane, 1st Bt, of Long Newton, County Durham by his (Tempest's) sister Frances. Long Newton had been purchased in 1635 by Sir Henry Vane of Raby (see Vane, Barons Barnard), and settled on his second son George in 1640.

The 3rd Marquess of Londonderry, having succeeded to the County Durham estates in right of his wife, added to them by purchase, the most notable acquisition being Seaham in 1821-2. Also in 1822 he bought Holdernesse (later Londonderry) House in London. On his death in 1854 the Irish estates passed to his son by his first marriage, as 4th Marquess, but the County Durham estates, after his second wife's death in 1865, to his son by her, George Vane (later Vane-Tempest) (1821-84). He succeeded his father as Earl Vane, by special remainder, and also succeeded as 5th Marquess to the Irish estates on the death of his half-brother in 1872. In 1846 he had married Mary, daughter and heir of Sir John Edwards, 1st Bt, of Garth and Plas Machynlleth (Montgomeryshire).

Following the death of the 7th Marquess in 1949 the County Durham estates passed to his son as 8th Marquess, and the Irish estates to his youngest daughter, Lady Mairi Bury. Londonderry House and the Welsh estates were sold (Plas Machynlleth being given to the town of Machynlleth).

Estates in 1883: Co Durham 12,823 acres, Montgomeryshire 7,399 acres, Merionethshire 2,685 acres, Co Down 23,554 acres, Co Londonderry 2,189 acres, Co Donegal 1,673 acres, total 50,323 acres worth £100,118 a year.