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.
Children
| Name | Birth | Death | Joined with |
| 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 | |
Footnotes (including sources)
| ‡ General |