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. The historic district includes the Ellicott City Station, which is the oldest surviving train station in the United States, having been built in 1830 as the first terminus of the original B&O Railroad line. The historic district is often called "Historic Ellicott City" or "Old Ellicott City" to distinguish it from the surrounding suburbs that extend south to Columbia and west to West Friendship.
In 1766, James Hood used the "Maryland Mill Act of 1669" to condemn 20 acres (8.1 ha) for a mill site adjacent to his river-side 157-acre (64 ha) property. His gristmill was built on the banks of the Patapsco River where the Frederick road (later known as the National Road, then U.S. Route 40, then Maryland Route 144) crossed the river. The site was later known as "Ellicott's Upper Mills". His son Benjamin rebuilt the corn grinding mill after one of the frequent Patapsco floods in 1768. Benjamin Hood then sold the mill to Joseph Ellicott in 1774 for 1,700 pounds.