Port Huron is a city in the U.S. state of Michigan and the county seat of St. Clair County. The population was 28,983 at the 2020 census. The city is bordered on the west by Port Huron Township, but the two are administered autonomously. Port Huron is located along the source of the St. Clair River at the southern end of Lake Huron. The city is along the Canada–United States border and directly across the river from Sarnia, Ontario.