Mont-Saint-Hilaire is an off-island suburb of Montreal in southeastern Quebec, Canada, on the Richelieu River in the Regional County Municipality of La Vallée-du-Richelieu. The population as of the Canada 2011 Census was 18,200. The city is named after the Mont Saint-Hilaire. A significant deposit of the semi-precious mineral sodalite is located near Mont-Saint-Hilaire.