The Rainy River is in Ontario.
Ontario . Almost all of Ontario 's 2700 km border with the United States follows inland waterways : from the west at Lake of the Woods , eastward along the major rivers and lakes of the Great Lakes/Saint Lawrence River drainage system . Rainy River is a town in north-western Ontario , Canada , southeast of Lake of the Woods . The Rainy River is a 22.5 mi river in Presque Isle County , Michigan , in the United States . The Rainy River ( French : Rivière à la Pluie ; Ojibwe : Gojiji-ziibi ) is a river , approximately 137 km long , which forms part of the Canada -- United States border separating northern Minnesota and Northwestern Ontario .