Mattoon is a city in Coles County, Illinois, United States. The population was 16,870 as of the 2020 census. The city is home to Lake Land Co…Mattoon is a city in Coles County, Illinois, United States. The population was 16,870 as of the 2020 census. The city is home to Lake Land College and has close ties with its neighbor, Charleston. Both are principal cities of the Charleston–Mattoon Micropolitan Statistical Area.