In early 1760s, James Montgomery built a log house on Glenthorne Tract. Years later, the present manor house was built. The house is five-bay, two-story, Federal style. It originally consisted of eight rooms with large central hall and a basement. The house has no footing, it sits solid on the ground starting with six bricks thick and tapering off. The house rises above a watertable pierced by windows retaining their original horizontal bars. The bricks are layed in Flemish bond design. The brick, nails, and shingles were hand made on place. Sixteen-by-twenty inch oak beams support the house. The beams were cut from a single tree and pit sawed, numbered, and pegged in place. All wood trim, doors, windows, and wainscoting was made by hand on place.
The windows throughout the first floor are nine over nine sash with brick jack arches. The second floor windows are nine over six sash with flat brick arches. Architrave trim and louvered shutters surround all the windows. A heavy, molded cornice extends across the north and south façades. The new entrance, located on the north façade has a Greek Revival doorway with sidelights, underpanels, and transom. A single-story porch with runs the length of the façade shelters the entrance. The porch, a later addition, consists of slender Doric columns connected by turned balusters supporting a plain frieze. The south façade also features an added two-story porch with Chinese lattice railing. Architrave trim and three-light transoms frame the entrances in both the first and second stories. Four interior chimneys with corbelled caps rise above the whole. The southwest chimney is nonfunctional and serves only to balance the design.
The main entrance opens into a center hall containing a single-run stair with two square balusters per tread, sawn-tread brackets, and recessed under-panels.
Glenthorne was altered in the late nineteenth century, the hall was widened, the stair moved, and a partition built creating two rooms out the single ballroom of originally eighteen by twenty foot. At that time, the symmetrically molded trim with corner blocks was added to the hall door and window openings. This trim, plus the doors, and stair in the first and second floor hallways are grained. During the late nineteenth century, the marbleized mantel was also added to the first floor northwest room. The mantel has channeled pilasters supporting a wide frieze, bed molding, and sawn shelf.
The rooms throughout the remainder of the house display their original woodwork. The fireplaces in the two first floor east rooms are set into projecting chimneybreasts and are decorated with mantels of recessed panels below a stacked bed molding. The woodwork in each room consists of recessed-rectangular paneled wainscot, flared recessed-paneled window jambs, and squeezed cyma trim at the openings.
The second floor west rooms are identical and both have recessed-panel wainscot. The northwest room is distinguished by its fireplace set in the paneled projecting chimney breast decorated with a shouldered architrave, plain frieze and stacked bed molding. The mantels have simple molded surrounds and shelves above slight, stacked bed molding.
The roof displays common-rafter construction with wrought and hand-headed machine cut nails. The rafters are mortise and tenoned, and connected by unusual diagonal braces running half the length of the building on each side. The attic has both of hand-hewn and up and down sawn beams.
The interior floors are original heart pine. The floor joists are three inches thick and sixteen inches wide. Some of the Cross and Bible design doors still have the original hand-forged hardware on them.
Originally, quite a few dependencies including the kitchen and workshop connect the house by brick walls. The first kitchen was in the yard with a covered brick walkway to the house. In 1914, a kitchen wing was added to the house. The beams in the ceiling of the newer kitchen are the original beams of a tobacco barn that stood five hundred feet southwest of the house. Water from a spring in an orchard southwest of the house ran by gravity into the kitchen. Two brick outbuildings were connected by a brick walk to the smokehouse, which still stands east of the house. A log outbuilding along with the tobacco barn was located on the hill south of the house. The Montgomery cemetery is 200 feet east of the house.