Ellicott City is an unincorporated community and census-designated place in, and the county seat of, Howard County, Maryland, United States. Part of the Baltimore metropolitan area, its population was 65,834 at the 2010 census, qualifying it as the largest unincorporated county seat in the country. Ellicott City's historic downtown – the Ellicott City Historic District – lies in the valleys of the Tiber and Patapsco rivers.