Breteuil Castle was built on a promontory overlooking the Valley of Chevreuse. The location was called “Bevilliers” after two villas or farms that were built on the site during the Gallo-Roman period. Before the Breteuil family settled on this land, their name appeared in Normandy in as early as the year 1100 when Guillaume (William) Osbern was made Count of Breteuil (Comte de Breteuil) by William the Conqueror. The latter considered Osbern as his most faithful companion and trusted him to the point of giving him the task of administering his English conquests when he returned to Normandy.
During this period a fortified castle replaced the two villas at Bevilliers. Today only its dovecote remains standing. The first owners successively bore the names of Choisel, Poissy and Plessis, Allemant, Hotman, and then Le Jay.
The last deed of sale of the properly called Bevilliers was signed in 1596. The seller was Nicolas Le Jay, the buyer Thibaut Desportes. A new castle was built with a square courtyard surrounded by a moat, an entrance pavilion and a drawbridge. The main building, overlooking a beautiful garden, stood at the far end of the courtyard. A careful observation of the moat reveals this first layout.
Morts sans enfants, les héritiers des Desportes sont d’abord des neveux Chanteclerc puis Renouard et enfin en 1712 Claude Charles de Breteuil qui épousera plus tard Laura O’Brien de Clare. Dès lors, le château sera transmis de père en fils dans cette famille.