EARLS AND MARQUESSES OF

LONDONDERRY  . The 1st earl of Londonderry was Thomas Ridgeway (c . 1565-1631), a Devon man, who was treasurer in Ireland from 16o6 to 1616 and was engaged in the plantation of Ulster . Ridgeway was made a baronet in 1611, Baron Ridgeway in 1616 and earl of Londonderry in 1623 . The Ridgeways held the earldom until March 1714, when Robert, the 4th earl, died without sons . In 1726 Robert's son-in-law, Thomas Pitt (c . 1688-1729), son of Thomas Pitt, " Diamond Pitt," governor at Madras and uncle of the great earl of Chatham, was created earl of Londonderry, the earldom again becoming extinct when his younger son Ridgeway, the 3rd earl of this line, died unmarried in January 1765 . In 1796 Robert Stewart (1739-1821), of Mount Stewart, Co . Down, was made earl of Londonderry in the Irish peerage . He had been created Baron Londonderry in 1789 and Viscount Castlereagh in 1795; in 1816 he was advanced to the rank of marquess of Londonderry . The 3rd marquess married the heiress of the Vane-Tempests and took the name of Vane instead of Stewart; the 5th marquess called himself Vane-Tempest and the 6th marquess Vane-Tempest-Stewart .