Isabel William was born circa 1405 in England to Mark William (-bef1434) and Agnes and died 14 April 1485 England of unspecified causes. She married John Seymour (c1406-1464) 30 July 1424 JL .
Children
| Name | Birth | Death | Joined with |
| John Seymour (c1425-c1463) | |||
| Margaret Seymour (c1428-) | |||
| Roger Seymour (c1430-bef1509) | 1430 England | 1509 England | Sibyl Hardin (c1462-) |
| Humphrey Seymour (c1430-1509) | |||
Siblings
| Name | Birth | Death | Joined with |
| Robert William (-bef 1424) | |||
| Isabel William (c1405-1485) | 1405 England | 14 April 1485 England | John Seymour (c1406-1464) |