Vaudreuil-Soulanges is a regional county municipality in Quebec, Canada. It is located on a triangular peninsula in the western Montérégie region of Quebec, surrounded by the Ottawa River to the north, the St. Lawrence River to the south, and Ontario to the west.
It is the only county in Quebec south of the Ottawa River, owing to the desire to keep the French-speaking population of the area within Lower Canada during the 1791 division of Upper and Lower Canada (precursors to the provinces of Ontario and Quebec). It is also geographically isolated from the Montérégie region, being its only county north of the St. Lawrence River.
Its name comes from the historical division of the area into two counties: "Vaudreuil" (named after Pierre François de Rigaud, Marquis de Vaudreuil-Cavagnal, governor of New France) for the communities along the Ottawa River, and "Soulanges" (named after Pierre-Jacques Joybert de Soulanges from Soulanges, Marne, France) for the communities along the St. Lawrence, a name of Québécois derivation referring to its southerliness. This division of the county into "Vaudreuil" and "Soulanges" still has salience today. The "Vaudreuil" area (consisting of the municipalities of Vaudreuil-Dorion, St-Lazare, Hudson, Rigaud, and others) is closer to Montreal and therefore more suburban, populous, and economically and ethnically diverse, compared to the Soulanges area (including the municipalities of St-Polycarpe, St-Zotique, Coteau-du-Lac, Rivière-Beaudette and Les Coteaux) which is solidly rural, agricultural, and linguistically French-Canadian.