Guillaume de Montfort (before 990 â before 1053) also known as Guillaume of Hainaut, was a French nobleman of the end of the 10th century, the first Lord of Montfort-l'Amaury.
He was succeeded as Lord of Montfort-l'Amaury by his son Amaury I de Montfort.
Guillaume is possibly the son of Amaury, Count of Valenciennes.