Southwestern Ontario is a subregion of Southern Ontario in the Canadian province of Ontario. It covers from the Bruce Peninsula in the north to Lake Erie in the south. From east to west, it goes from Guelph to Windsor. London is the largest city in the region.
In 2011 the population of the region was 2,504,878. Agriculture and auto manufacturing are a large parts of the region's economy. Much of Canada's trade with the eastern and midwestern United States passes through southwestern Ontario.