Ellicott City is an unincorporated community and census-designated place in, and the county seat of, Howard County, Maryland, United States. It is part of the Baltimore metropolitan area. The population was 65,834 at the 2010 census. Founded in 1772, the town contains the B. & O. Railroad Museum's branch at the Ellicott City Station, built in 1830 as the first terminus of the initial line. The downtown historic district is located in the valley of the small Tiber River, with its east end abutting the Patapsco River, which forms the Baltimore County line. As of the 2000 census, Ellicott City surpassed Towson (county seat of neighboring Baltimore County) for the first time, as the largest unincorporated county seat in the country.
The downtown area in the Patapsco Valley is often called "Historic Ellicott City" or "Old Ellicott City", to distinguish it from the surrounding suburban unincorporated area that extends south to the other large unincorporated town in Howard County, Columbia, and west to West Friendship. It is listed on the National Register of Historic Places as Ellicott City Historic District. Wikipedia