Mary of Lancaster was born circa 1320 in Tutbury Castle, Staffordshire, England, United Kingdom to Henry Plantagenet, 3rd Earl of Lancaster (1281-1345) and Matilda de Chaworth (1282-1322) and died 1 September 1362 Alnwick, Northumberland, England, United Kingdom of unspecified causes. She married Henry de Percy, 3rd Baron Percy (1320-1368) 1334 JL in Tutbury Castle, Staffordshire, England, United Kingdom. Alfred the Great (849-899)/s, Charlemagne (747-814)/s, Henry II of England (1133-1189)/s, Hugh Capet (c940-996)/s, William I of England (1027-1087)/s, Rollo of Normandy (860-932)/s.
|Offspring of Henry, 3rd Baron Percy of Alnwick and Mary of Lancaster (c1320-1362)|
|Henry Percy, 1st Earl of Northumberland (1341-1408)||10 November 1341 England, United Kingdom||20 February 1408 Bramham Moor, Yorkshire, England||Margaret Neville (1329-1372)|
|Thomas Percy, 1st Earl of Worcester (1343-1403)||1343||23 July 1403 Shrewsbury, Shropshire, England, United Kingdom|