The property, about 1 acre (0.40 ha) in size, is fringed on the front and east side by a low stone retaining wall.

The front facade is five bays wide, with a center entrance sheltered by a gabled portico supported by Doric columns.

The interior follows a central hall plan, with a parlor and study on the left, and a large dining room and serving chamber on the right; the kitchen is located in the basement.

Johnson was influential in relations between the colonial government and the local Mohawk people, and was named the crown Superintendent of Indian Affairs in 1756.

After passing through many owners, Fort Johnson was purchased in the 1920s by John Watts DePeyster and given to the Montgomery County Historical Society, which now operates it as a museum.