St. Mary's was the site of a planned village within early Victoria County, in the Canadian province of Ontario. The site was laid aside in the surveying of the county in the 1830s, but was later found to be unusable when limestone was discovered two inches below the ground. Today its site marks one end of a man-made canal between Balsam Lake and Lake Simcoe, part of the Trent-Severn Waterway.