Marlborough is a town in Hartford County, Connecticut, United States. It contains the census-designated place of Terramuggus. The town is part of the Capitol Planning Region. The town's population was 6,133 at the 2020 census. Marlborough is a suburban and rural community. The local high school is RHAM High School. In 2013, Marlborough ranked third in Connecticut Magazine's biannual ranking of Connecticut small towns.