Joan, Countess of Ponthieu

Joan of Dammartin (c. 1220–1279), queen of Castile and countess of Ponthieu, was the eldest daughter of Simon of Dammartin and Marie of Ponthieu. In 1234 she was promised to Henry III of England, but the pope forbade the match on grounds of kinship.

In 1237 Joan married Ferdinand III of Castile; her daughter Eleanor married Edward I of England. Widowed in 1252, she ruled Ponthieu and from 1263 Aumale, then married Jean de Nesle, running up substantial debts. She died at Abbeville in 1279, leaving Ponthieu to Eleanor and Aumale to her grandson John I.