The founder of the family fortune was Sir Edward Trevor though the name Trevor became fixed in the time of John Trevor (d. 1453). Sir Edward went to Ireland, with Edward Blayney of Gregynog, Montgomeryshire, as a Captain in the expedition sent to Ireland after the Battle of the Yellow Ford in 1598. He married secondly Rose, daughter of James Ussher, archbishop of Armagh, and acquired an estate in County Down, which he called Rostrevor. In 1619 he built the present mansion of Brynkinalt, later enlarged by the 2nd Viscount Dungannon. Sir Edward died in Ireland in 1642 and was succeeded by his eldest son John Trevor who died in about 1643. Sir Mark Trevor (1618-1670), one of Sir Edward's sons by his second marriage was created 1st viscount Dungannon and Baron Trevor of Rostrevor in 1662. John Trevor's son, Sir John Trevor (1638-1717), became Speaker of the House of Commons and Master of the Rolls. With the death of his son in 1762 the male line came to an end and the estates passed to his daughter, Anne, the sole heiress, who married Michael Hill, of Hillsborough, County Down, Ireland. The estates then passed to their second son, Arthur Hill (d. 1771), who on succeeding to the lands in 1763, took on the additional surname of Trevor. Arthur was created viscount Dungannon of the second creation in 1765. Arthur Hill-Trevor (d. 1771) was succeeded by his grandson, Arthur Hill-Trevor (1763-1837), 2nd viscount Dungannon. His son, Arthur Hill-Trevor (1798-1862), 3rd viscount Dungannon, was the last of the male line and on his death the Brynkinalt and other estates devolved on his kinsman, Lord Arthur Edwin Hill (1819-1894), 1st Baron Trevor of Brynkinalt, who was the third son of Arthur, 3rd Marquis of Downshire, and great-grandson of Ann Trevor's elder son, Trevor Hill, 1st viscount Hillsborough, the title of viscount Dungannon becoming extinct. Lord Arthur assumed by royal licence the additional surname and arms of Trevor on succeeding to the Brynkinalt estate. He was created a peer in 1880. The estate and title then descended in the male until the present occupier, Charles Edwin Hill-Trevor (b. 1928), 4th Baron Trevor.
Scope and content: Deeds, 1511-1956, relating to lands in Denbighshire, 1588-1944, Flintshire, 1655-1914, Middlesex, 1603-1898, mainly Fulham, 1699-1895, and Knightsbridge, 1603-1909, and Shropshire, 1511-1929, mainly in St Martin's; surveys, rentals and particulars, [late 19 cent.]-1949; accounts and vouchers, [mid 17 cent.]-1953; inventories and valuations, 1838-1928; estate correspondence, 1680-1941, including estate letter books, 1888-1927; plans, [c. 1808]-1931; sale plans and particulars, 1862-1929, papers relating to coal mining in Flintshire, 1857-[late 19 cent.]; family probate records, 1674-1887; and legal records, 1684-1921.