Career
He was a royal notary, and, as one of the King's men, a canon of the cathedrals of Laon, Noyon, Senlis, Mello, Marchais and of Reims, archdeacon of Laon and of Thiérache. He derived his name from his small seigneurie of Ercuis (Old French Arcuys or Erquez. Latin Arquetum) in the Beauvaisis between Neuilly-en-Thelle and Cires-lès-Mello, about 55 km from Paris.
At Ercuis he erected a chapel dedicated to Virgin Mary, served by the monks of the Abbey of St Genevieve, Paris. Guillaume d'Ercuis kept a journal, his livre de raison noting his expenses for the purchase of domains, of furnishings and books. Some annotations relate to his personal life and to court life.
His descendent, H. Coustant d'Yanville, published a Notice sur Guillaume d'Ercuis, précepteur de Philippe le Bel (Beauvais 1864).