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is a charter township of St. Clair County in the U.S. state of Michigan. The population was 10,691 at the 2000 census.
According to the United States Census Bureau, the township has a total area of 16.1 square miles (41.7 km²), of which, 16.1 square miles (41.6 km²) of it is land and 0.04 square miles (0.1 km²) of it (0.19%) is water.
Fort Gratiot is on the southwestern shore of Lake Huron and is considered to be part of the Thumb of Michigan, which in turn is a subregion of the Flint/Tri-Cities. Fort Gratiot is a major center of trade for the Blue Water Area, a subregion of the Thumb. The Birchwood Mall and many other big box stores are located in Fort Gratiot.