Guillaume d'Ercuis (1265 — 1314/15) was the almoner to King Philip III of France and the tutor of his son, King Philip IV. 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.
His parents were Guillaume d’Ercuis (1240-1302) and Helisende. His brother was called Jean; he was a servant to Philip IV.
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).
- His will is dated 1314.
- Margaret Bent, Andrew Wathey: Fauvel studies: allegory, chronicle, music, and image in Paris, Bibliothèque nationale de France.
- Lalou Élisabeth, Les notaires du Roi sous Philippe le Bel, un milieu social parisien?
- The Middle Ages by Frantz Funck-Brentano. 1925, p. 854.
- Conserved in the Bibliothèque Sainte-Geneviève, Paris, ms. 2025; edited and published by Joseph Petit, De libro rationis Guillelmi de Erqueto, (Paris) 1900.
- Coustant d'Yanville H., Notice sur Guillaume d'Ercuis, précepteur de Philippe le Bel, Beauvais, 1864