William de Harcourt was born circa 1100 in Normandy, France to Robert de Harcourt (c1034-aft1100) and Colette d'Argouges and died circa 1148 England of unspecified causes. He married Agnes d'Ambroise (-c1141) .
Collins's peerage of England; genealogical, biographical, and historical, Volume 4 by Arthur Collins, Sir Egerton Brydges
"William de Harcourt, eldest son of Robert, before mentioned, taking part with Henry I. against his brother Robert Curtois aforesaid, commanded the troops which defeated Walleran de Beaumont, Earl of Mellent, in the battle near Bourgtouroude, A. D. 1123, and for services was rewarded with large possessions in England. He wedded Hue D'Amboise, by whom he had three sons, and two daughters; viz. Robert de Harcourt, Ivo de Harcourt, of both of whom more amply; Simon de Harcourt, who married Adeliza, daughter and coheir of Osbert de Arden, of Kingsbury, in Warwickshire, but died without issue; Peretta, the wife of John, Lord of Hellenvillier, in France; and Beatrix, espouses to Robert Basset."
Children
| Name | Birth | Death | Joined with |
| Robert de Harcourt | |||
| Ivo de Harcourt (c1130-1180) | 1130 England | 1148 England | Agnes Unknown |
| Simon de Harcourt | |||
| Peretta de Harcourt | |||
| Beatrix de Harcourt | |||
Siblings
| Name | Birth | Death | Joined with |
| William de Harcourt (c1100-c1148) | 1100 Normandy, France | 1148 England | Agnes d'Ambroise (-c1141) |
| Richard de Harcourt | |||
| Philip de Harcourt (-1163) | |||
| Henry de Harcourt | |||
| Baldwin de Harcourt | |||
| Errand de Harcourt | |||
| Rollo de Harcourt | |||