| Montfort-l'Amaury | |
| Commune Status: | Commune |
| Image Coat Of Arms: | Arms of Montfort-l'Amaury.svg |
| Arrondissement: | Rambouillet |
| Canton: | Aubergenville |
| Insee: | 78420 |
| Postal Code: | 78490 |
| Mayor: | Hervé Planchenault[1] |
| Term: | 2020 - 2026 |
| Intercommunality: | CC Cœur d'Yvelines |
| Demonym: | Montfortois |
| Coordinates: | 48.7778°N 1.81°W |
| Elevation Min M: | 98 |
| Elevation Max M: | 183 |
| Area Km2: | 5.71 |
Montfort-l'Amaury (pronounced as /fr/) is a commune in the Yvelines department in the Île-de-France region, Northern France. It is located 20km (10miles) north of Rambouillet. The name comes from Amaury I de Montfort, the first seigneur (lord) of Montfort.
Montfort-l'Amaury lies north of the Rambouillet Forest. It is located at the foot of low hills, at about 130 m above sea level.
King Robert II built a castle in 996 in the hills of Montfort. Montfort-l'Amaury was the stronghold of the Montfort family from the start of the 11th century. Amaury I built the ramparts.
The Comté de Montfort was related to the Duchy of Brittany following the marriage of Yolande de Dreux-Montfort with Arthur of Brittany in 1294. It returned to the crown of France when Brittany became a part of France under Francis I. The castle was destroyed by the English during the Hundred Years' War.