The Cornwall Canal was built in 1834, to facilitate travel to the upper St Lawrence basin and the Great Lakes. Unfortunately, the canal cut the town off from the mainland, creating an island in the middle of the river. Over time, the village expanded to the north, eventually forming one town that was split in the middle into "old" Mille Roches on one side of the canal and "new" Mille Roches on the mainland to the north. The canal's course caused the decline of the village and the area only improved with the arrival of railways in the 1850s.