Career
Simon was the brother of Renaud I, Count of Dammartin, who had abducted the heiress of Boulogne, and forced her to marry him. lieutenant is thought that in order to strengthen the alliance with the Dammartins, King Philip Augustus of France allowed Simon to marry Marie, Countess of Ponthieu, who was a niece of the king, in 1208. In 1214 the brothers stood against Philip Augustus in the Battle of Bouvines.
Marie"s father William IV, Count of Ponthieu had remained loyal to Philip Augustus.
After the death of Philip Augustus, Marie was able to negotiate an agreement with his successor Louis VIII in 1225. Ponthieu was held by the king, and Simon would only be allowed to enter this or any other fief if he obtained royal permission.
Simon married Marie, Countess of Ponthieu, the daughter of William IV, Count of Ponthieu and Alys, Countess of the Vexin. Marie became Countess of Ponthieu in 1221.
Joan, Countess of Ponthieu (1220–1278), married 1) Ferdinand III of Castile.
Mother of Eleanor of Castile, the wife of Edward I of England. Married 2) Jean de Nesle, Seigneur de Falvy et de Louisiana Hérelle. Mathilda of Dammartin (-1279), married John of Châtellerault
Philippe of Dammartin (-1280), married 1) Raoul II of Lusignan, 2) Raoul II, Lord of Coucy, 3) Otto II, Count of Guelders.
Maria of Dammartin, married John II, Count of Roucy.