The St. Marys River, St. Mary's River, or St. Mary River may refer to:
Canada St. Mary River (British Columbia), tributary of the Kootenay River St. Mary's River (Nova Scotia), an important Nova Scotia salmon river
United States St. Marys River (Florida–Georgia), forming a portion of the boundary between Georgia and Florida St. Marys River (Indiana and Ohio), tributary of the Maumee River St. Marys River (Maryland), tributary of the Chesapeake Bay Saint Marys River (Virginia), tributary of the South River
Multi-national St. Mary River (Alberta–Montana), tributary of the Saskatchewan River in Montana and Alberta St. Marys River (Michigan–Ontario), connecting Lake Superior and Lake Huron and forming a portion of the international boundary between the U.S. and Canada
See also Mary River (disambiguation) Marys River (disambiguation) Saint Maries River St. Mary's (disambiguation)