Port Huron (hyŏrˈən) [key], city (1990 pop. 33,694), seat of St. Clair co., S Mich., a natural, deepwater port of entry at the junction of the St. Clair River with Lake Huron; inc. 1857. It is a shipping center with railroad shops and plants that manufacture transportation equipment, building materials, machinery, salt, metal and paper products, chemicals, consumer goods, and electrical equipment. The earliest European settlement began (1686) with the French fort St. Joseph. The town grew after the building (1826) of Fort Gratiot Turnpike (between Port Huron and Detroit), ushering in a lumbering era. Local deposits of salt, oil, and natural gas were developed. Port Huron is connected by a railway tunnel and an international bridge with Sarnia, Ont. The old Fort Gratiot lighthouse marks the St. Clair straits off Port Huron. Thomas Edison grew up in the city.