Allegan is a city in the U.S. state of Michigan. The population was 4,998 at the 2010 census. It is the county seat of Allegan County. The city lies within Allegan Township, but is administratively autonomous.Allegan was named in a neologism by Michigan historian Henry Rowe Schoolcraft in 1837 to sound like a Native American word. Land was purchased from government to form the downtown business district; village organization came in 1838 with city incorporation authorized in 1907.Allegan is located in the south-central portion of the county. To the west and northwest is the nearly 50,000 acre forest Allegan State Game Area for which the city is considered a gateway. Lake Allegan in Valley Township is also a great tourist destination for boating, fishing, and swimming activities.Allegan's dense forests, lakes, and river geography served as a source of water power, trade routes for steamboats and timber production.