The calculated distance (air line) between Saint-Joseph-du-Lac and Longueuil is approximately 26 miles respectively 41 kilometers.
By car or train, the actual journey to Longueuil is certainly longer, as only the direct route (as the crow flies) between Saint-Joseph-du-Lac and Longueuil has been calculated here.
Air line (approximately)
41 kilometers
22 nautical miles