Tecumseh, Michigan. Downtown Tecumseh. Tecumseh is a small city in Lenawee County, Michigan, United States. It is situated where M-50 crosses the River Raisin, a few miles east of M-52. Tecumseh is about 60 miles (97 km) southwest of Detroit, 25 miles (40 km) south of Ann Arbor and 40 miles (64 km) north of Toledo, Ohio.