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 75,947 at the 2020 census, making it the most populous 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.