Sarnia is a city located in Lambton County, Ontario, Canada. It serves as the largest city on Lake Huron and is situated in the Southwestern Ontario region.
The city is positioned on the eastern bank of the junction where Lake Huron flows into the St. Clair River. This location forms part of the Canada–United States border, placing Sarnia directly across from Port Huron, Michigan. As of 2021, the city had a population of 72,047.