London is a city in southwestern Ontario, Canada, along the Quebec City–Windsor Corridor. The city had a population of 422,324 according to the 2021 Canadian census. London is at the confluence of the Thames River and North Thames River, approximately 200 km (120 mi) from both Toronto and Detroit; and about 230 km (140 mi) from Buffalo, New York. The city of London is politically separate from Middlesex County, though it remains the county seat.

The Quebec City–Windsor Corridor is the most densely populated and heavily industrialized region of Canada. As its name suggests, the region extends between Quebec City in the northeast and Windsor, Ontario, in the southwest, spanning 1,150 kilometres (710 mi). With more than 18 million people, it contains about half of the country's population, three of Canada's four largest metropolitan areas and seven of Canada's twelve largest metropolitan areas, all based on the 2016 census. Its relative importance to Canada's economic and political infrastructure renders it akin to the Northeast megalopolis in the United States. The name was first popularized by Via Rail, which runs frequent passenger rail service in the region in its service area known as "The Corridor".