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.

King's Highway 401, commonly referred to as Highway 401 and also known by its official name as the Macdonald–Cartier Freeway or colloquially referred to as the four-oh-one, is a controlled-access 400-series highway in the Canadian province of Ontario. It stretches 828 kilometres (514 mi) from Windsor in the west to the Ontario–Quebec border in the east. The part of Highway 401 that passes through Toronto is North America's busiest highway, and one of the widest. Together with Quebec Autoroute 20, it forms the road transportation backbone of the Quebec City–Windsor Corridor, along which over half of Canada's population resides. It is also a Core Route in the National Highway System of Canada. The route is maintained by the Ministry of Transportation of Ontario (MTO) and patrolled by the Ontario Provincial Police. The speed limit is 100 km/h (62 mph) throughout its length, with the only exceptions being the posted 80 km/h (50 mph) limit westbound in Windsor and in most construction zones, along with a 110 km/h (68 mph) speed limit between Windsor and Tilbury.