Casco is a town in Cumberland County, Maine, United States. The population was 3,742 at the 2010 census. Casco includes the villages of Casco, South Casco and Cook Mills. The town borders the east shore of Sebago Lake, and is home to part of Sebago Lake State Park. Casco is part of the Portland?South Portland?Biddeford, Maine metropolitan statistical area. Casco is just under 30 miles from downtown Portland.Casco is the home of "Casco Days", an annual community fair which takes place in Casco Days Park, always on the last Saturday in July.