Percy was the eldest son of Algernon Percy, 10th Earl of Northumberland (1602-1668), Knight of the Order of the Garter, by his second wife, Elizabeth Howard, daughter of Theophilus Howard, 2nd Earl of Suffolk (1584-1640), Knight of the Order of the Garter.
He served as a Page of Honour at the coronation of King Charles II on 23 April 1661 and on 4 November 1661 entered the Inner Temple for legal training. Topcliffe Castle, Yorkshire, recorded in the Domesday Book of 1086 as held by William I de Percy (d1096), whom it served as the caput of the feudal barony of Topcliffe. The Percy family"s most ancient English seat.
Petworth, Sussex, acquired by Joscelin of Louvain (d1180), husband of Agnes de Percy, one of the two daughters and co-heiresses of William II de Percy (d1174/5), feudal baron of Topcliffe in Yorkshire (grandson of William I de Percy (d1096)).
Jocelin"s younger son Richard "de Percy" (d1244) adopted the surname "de Percy" and inherited his father"s estate of Petworth and a moiety of his maternal barony of Topcliffe. Alnwick Castle, Northumberland, purchased in 1309 by Henry de Percy, 1st Baron Percy (1273–1314) from Anthony Bek, Prince Bishop of Durham.
Warkworth Castle, Northumberland Egremont Castle, Cumbria, purchased in 1529 by Henry Percy, 15th Earl of Northumberland from Robert Radclyffe, 1st Earl of Sussex (1483–1542). Leconfield Castle, Yorksire.
Syon House, Isleworth, Middlesex, the former Syon Monastery, acquired in 1594 by Henry Percy, 9th Earl of Northumberland (1564-1632).
