Dammartin, medieval French countship, whose seat was at Dammartin-en-Goële, northwest of Meaux (in the modern département of Seine-et-Marne).
Hugh, the first recorded count, built a castle in the area in the 10th century. In the 11th and 12th centuries its possessors were strong enough to oppose either the French kings or the counts of Flanders. Raynald I of Dammartin, who was also count of Boulogne, was a member of the great coalition crushed by Philip II Augustus of France at the Battle of Bouvines in 1214; he killed himself in prison in 1227. Seized by the king, Dammartin then passed to his son Philip Hurepel and thereafter passed through a number of families, coming finally into the hands of Antoine de Chabannes in 1439. This Antoine de Chabannes (d. 1488), who had already distinguished himself in campaigns with Joan of Arc, later became a leader of the Ecorcheurs and fought against Louis XI in the League of the Public Weal and then for Louis against the Burgundians. His great-granddaughter Françoise d’Anjou-Mézières, however, left heirs by both of her marriages, and one family sold Dammartin to the Montmorencys while the other sold it to the Guises. There followed a long lawsuit, which the Montmorencys won. King Louis XIII confiscated the countship after the treason of Henry de Montmorency (1632), had the castle dismantled, and finally gave the property to the House of Condé.