Sarnia is a city in Southwestern Ontario, Canada, and had a 2011 population of 72,366. It is the largest city on Lake Huron and in Lambton County. Sarnia is located on the eastern bank of the junction between the Upper and Lower Great Lakes where Lake Huron flows into the St. Clair River, which forms the Canada-United States border, directly across from Port Huron, Michigan. The city's natural harbour first attracted the French explorer La Salle, who named the site "The Rapids" when he had horses and men pull his 45-tonne barque "Le Griffon" up the almost four-knot current of the St.