Port Huron is a city and county seat of St. Clair County, Michigan, United States. The population was 28,983 at the 2020 census. The city is bo…Port Huron is a city and county seat of St. Clair County, Michigan, United States. 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.