Coteau-du-Lac is a small city in southwestern Quebec, Canada. It is on the north shore of the St. Lawrence River in the Vaudreuil-Soulanges Regional County Municipality.The name of the town comes from the French word Coteau which meant "slope" and from its location on the north shore of Lake Saint Francis. The National Historic Site of Canada of the Coteau-du-Lac canal is the location of the first canal lock system in North America.