Lake Mattoon is a 1,050-acre (4.2 km²) reservoir located in Coles County, Illinois, Cumberland County, Illinois, and Shelby County, Illinois. Almost three-quarters of the lake, 765 acres (3.1 km²), is located in Shelby County. The reservoir was built to supply tap water to Mattoon, Illinois and Neoga, but also provides fishing and boating recreation.