Old Longueuil usually refers to the pre-1961 city of Longueuil. Occasionally, Old Longueuil may also include the former territory of Montréal-Sud (except Downtown Longueuil).
Old Longueuil, was named a heritage district by the city in 1993, and features 450 buildings built before 1945. Many historic buildings are found in this district, such as the Co-Cathedral of Saint-Antoine-de-Padoue, the ruins of Fort Longueuil, and Saint Mark's Anglican Church. Rue Saint-Charles is the main street in this neighbourhood and features many small businesses, among them restaurants, bars, and corner stores. The borough hall of Le Vieux-Longueuil borough is also in the neighbourhood.