St. Joseph is a township in the Canadian province of Ontario, the largest of four municipalities on St. Joseph Island. It had a population of 1,240 in the Canada 2016 Census.

St. Joseph Island is in the northwestern part of Lake Huron. It is part of the Canadian province of Ontario. At 365 km2 (141 sq mi) in area, it is the sixth largest lake island in the world; the second largest island on Lake Huron, following Manitoulin Island; and the third largest of all the islands on the Great Lakes, trailing Manitoulin and Lake Superior's Isle Royale.