Mary, Countess of Blois

Mary of Avesnes (c. 1200–1241), countess of Blois, was the only child of Walter II d'Avesnes and Margaret of Blois. In 1225 she married Hugh I of Châtillon; the couple founded the nunnery of Pont-aux-Dames.

On her mother's death in 1230 she inherited the County of Blois, holding also lands including Avesnes and Guise as her parents' sole heiress; Hugh ruled Blois with her. She died in 1241, and Blois passed to her eldest son John I. Her son Guy became count of Saint-Pol.