Carroll County is bordered on the north by the Mason-Dixon Line. The Patapsco River forms the southern border and Liberty Reservoir forms part of the eastern border. Carroll County is bordered on the west by the Monocacy River and Sam's Creek. Carroll has 8 incorporated municipalities: Taneytown, Hampstead, Manchester, Mount Airy, New Windsor, Sykesville, Union Bridge, and Westminster, which is the County Seat. Carroll County is located within the Baltimore Metropolitan Area, which is the nation's 20th largest market, with over 2.6 million people. Located in the heart of the Mid-Atlantic on the east coast, the Baltimore Metropolitan Area also includes Baltimore City, Anne Arundel County, Baltimore County, Harford County, Howard County, and Queen Anne’s County. Carroll County is governed by five commissioners, each representing his or her home district.