Windsor is a city in southwestern Ontario, Canada, on the south bank of the Detroit River directly across from Detroit, Michigan, United States. Geographically located within but administratively independent of Essex County, it is the southernmost city in Canada and marks the southwestern end of the Quebec City–Windsor Corridor. The city's population was 229,660 at the 2021 census, making it the third-most populated city in Southwestern Ontario, after London and Kitchener. The Detroit–Windsor urban area is North America's most populous trans-border conurbation, and the Ambassador Bridge border crossing is the busiest commercial crossing on the Canada–United States border.