Earl of Londonderry extinct on the death of his great-grandson, the fourth Earl, in 1714. The second creation came in 1726 in favour of the soldier and politician Thomas Pitt, 1st Baron Londonderry. He had already been created Baron Londonderry in 1719 and was made Viscount Gallen-Ridgeway at the same time as he was granted the earldom, also in the Peerage of Ireland. He was the husband of Lady Frances Ridgeway, daughter and heiress of the fourth Earl of the first creation. A member of the prominent Pitt family, he was the uncle of William Pitt, 1st Earl of Chatham. His younger son,
James Sinclair, 12th Earl of Caithness Ross-shire militia. He married at Thurso Castle on 2 January 1784 Jane, second daughter of Alexander Campbell of Bareldine who was deputy governor of Fort George. They had the following children: James Sinclair, 12th Earl of Caithness James Sinclair, 12th Earl of Caithness was a Scottish noble and chief of the Clan Sinclair. James Sinclair was born at Barrogill Castle (Castle of Mey) on 31 May 1766. He was the son of Sir John Sinclair of Mey, Baronet who he succeeded in the baronetcy in 1774. He succeeded as 12th earl of Caithness in 1789, as nearest lawful male heir