Longueuil is a city in located in the Montérégie administrative region of Quebec, and part of Greater Montreal. It sits on the south shore of the Saint Lawrence River directly across from Montreal, in southwestern Quebec. The population as of the Canada 2006 Census totaled 229,330, making it the fifth most populous city in Quebec and 19th largest in Canada. The city comprise three boroughs: Vieux-Longueuil, Saint-Hubert and Greenfield Park. It is also the second-largest suburb of Montreal.
Residents of Longueuil are known as Longueuillois.