Ellicott City is an unincorporated community and census-designated place, along with being the county seat of local government in Howard County, Maryland, United States. It is part of the Baltimore–Washington Metropolitan Area. The population was 65,834 at the U.S. Decennial Census of 2010. It is the county seat of Howard County. Founded in 1772, the town contains the B. & O. Railroad Museum's branch at the Ellicott City Station, built in 1830, and the first terminus of the initial line. The downtown historic district is located in the valley of the upper Western Branch of the Patapsco River. As of the 2000 U.S. Census, Ellicott City surpassed Towson, Maryland (county seat of neighboring Baltimore County) for the first time, as the largest unincorporated county seat in the country.