Châteaudun is a commune in the Eure-et-Loir department in northern France. It is a sub-prefecture of the department. It was the site of the …Châteaudun is a commune in the Eure-et-Loir department in northern France. It is a sub-prefecture of the department. It was the site of the Battle of Châteaudun during the Franco-Prussian War. Châteaudun is located about 45 km northwest of Orléans, and about 50 km south-southwest of Chartres. It lies on the river Loir, a tributary of the Sarthe.