Mary de Thornton was born circa 1324 in England to Peter de Thornton (c1290-1358) and Lucia de Hellesby (c1297-1335) .
Mary died unmarried and no children.
Siblings
| Name | Birth | Death | Joined with |
| Ellen de Thornton (c1316-1355) | 1316 England | 1355 England | Thomas de Dutton (1315-1381) |
| Margaret de Thornton (c1318-) | 1318 England | William de Golborne | |
| Emma de Thornton (c1320-) | 1320 England | Hugh de Weverham | |
| Katherine de Thornton (c1322-) | 1322 England | ||
| Mary de Thornton (c1324-) | 1324 England | ||
| Elizabeth de Thornton (c1326-) | 1326 England | Hamon Fitton of Bollin | |
| Maud de Thornton (c1328-) | 1328 England | Henry Beeston of Beeston | |