The Saint Louis River (abbreviated St. Louis River) is a river in the U.S. states of Minnesota and Wisconsin that flows into Lake Superior. The largest U.S. river to flow into the lake, it is in length and starts east of Hoyt Lakes, Minnesota. The river's watershed covers . Near the Twin Ports of Duluth, Minnesota and Superior, Wisconsin, the river becomes a freshwater estuary. According to Warren Upham, the Ojibwe name of the river is Gichigami-ziibi (Great-lake River). He notes:

"The river was probably so named by Pierre Gaultier de Varennes, sieur de La Vérendrye (1685–1749), who was a very active explorer, in the years 1731 and onward, of the vast country from Pigeon River and Rainy Lake to the Saskatchewan and Missouri Rivers, establishing trading posts and missions. The king of France in 1749, shortly before the death of La Vérendrye, conferred on him the cross of Saint Louis as a recognition of the importance of his discoveries, and thence the name of the Saint Louis River appears to have come. On Jean-Baptiste-Louis Franquelin's map (1688) and Philippe Buache's map (1754), it is called the Rivière du Fond du Lac, and the map by Gilles Robert de Vaugondy (1755) and Jonathan Carver's map (1778) are the earliest to give the present name."