Harmony Hall is in the Broad Creek Historic District, the first historic district formed under Prince George's County preservation law. The house is an 18th century Georgian country house that architecturally ranks as one of the great early plantation houses and an outstanding early colonial house of Maryland. The front of the house faces the Potomac River and remains much as it appeared in 1766, the estimated time of construction.

Harmony Hall was acquired by the National Park Service in 1966 under the provisions of the Capper-Crampton Act of 1930, and was listed on the National Register of Historic Places in 1980.