The Grand River, formerly known as the River Ouse, is a large river in Ontario, Canada. It lies along the western fringe of the Greater Golden Horseshoe region of Ontario which overlaps the eastern portion of southwestern Ontario, sometimes referred to as Midwestern Ontario, along the length of this river. From its source near Wareham, Ontario, it flows south through Grand Valley, Fergus, Elora, Waterloo, Kitchener, Cambridge, Paris, Brantford, Ohsweken, Six Nations of the Grand River, Caledonia, and Cayuga before emptying into the north shore of Lake Erie south of Dunnville at Port Maitland. One of the scenic and spectacular features of the river is the falls and Gorge at Elora.

The Golden Horseshoe is a secondary region of Southern Ontario, Canada, which lies at the western end of Lake Ontario, with outer boundaries stretching south to Lake Erie and north to Lake Scugog, Lake Simcoe and Georgian Bay of Lake Huron. The region is the most densely populated and industrialized in Canada. Based on the 2021 census, with a population of 7,759,635 people in its core and 9,765,188 in its greater area, the Golden Horseshoe accounts for over 20 percent of the population of Canada and more than 54 percent of Ontario's population. It is part of the Quebec City–Windsor Corridor, itself part of the Great Lakes megalopolis.