Designed by John Kimball, Sr., an architect/housewright from Ipswich, Massachusetts, the McLellan-Sweat Mansion is an excellent example of Federal-style architecture. The house was built for shipping magnate Major Hugh McLellan. It is a three-story rectangular brick building laid in Flemish bond, a pattern that alternates the long and short sides of the brick. The symmetrical facade is dominated by an elaborate semicircular entry porch supported by Doric columns and topped by a balustrade or railing.

The Powers House is a large post and beam constructed late Colonial era building. Sheathed in unfinished clapboard siding and resting on a fieldstone foundation, the house has a hipped roof and large internal chimneys on each side. The facade is symmetrical with a central entry door. The door is framed by sidelight windows and a molded lintel. The windows are made up of multiple small panes. The eaves overhang the slightly smaller second floor windows. A one-story ell extends off the south elevation.

Thought to be the oldest known dwelling in Calais, the Holmes Cottage is a one-and-a-half story building with a side-gabled roof and a large central chimney. The front facade is dominated by a projecting vestibule added in the late nineteenth century. The wood framed and clapboard sheathed structure sits on a fieldstone foundation on Main Street. Local folklore dates the house to 1805-an era when the community was small and with little means. What is more likely, however, is that the house was not built until c.1820 when the lumber industry developed in Calais.

Construction on the Sargent-Roberts House began in 1814. Originally a simple Federal-style dwelling, the house, located on State Street, went through many renovations in the nineteenth century. A few characteristics of the original design remain including the symmetrical facade with a central door flanked by two single windows. Edward Sargent sold the house to Amos M. Roberts during the 1830s. Roberts, a wealthy lumberman and banker, began adding more opulent features to the three-story dwelling.

Located in Fort Point State Park, Fort Pownall looks out to where the Penobscot River meets Penobscot Bay. Originally the outer walls of the fort were ninety feet long and ten feet high and surrounded by a moat fifteen feet wide and eight feet deep with palisades placed in the middle for more protection. A drawbridge was used to enter the fort. Within the walls was a forty-four-foot blockhouse standing two-stories tall with diamond shaped flankers at each corner for riflemen. The whole fort was constructed of squared timbers, dovetailed at the corners and tree-nailed.

The First Baptist Church is an early nineteenth-century building that exhibits Greek Revival-style features resulting from extensive remodeling in 1849. The house of worship is a two-story rectangular wooden framed building sitting on a granite slab and sheathed in weatherboards. It features a gable-front pediment, corner pilasters, and broad entablatures above the pair of widely spaced front doors. The doors are flanked by wide pilasters and multi-light transoms and topped with broad entablatures. The windows are double-hung sash with many small panes of glass with functional shutters.

Located in the Acadian Village on Route 1 in Van Buren, the Roy House was originally located in Hamlin, Maine, and moved to its current location after 1977. The log house features piece-on-piece (or pice sur pice) construction with hand-hewed or squared timber stacked together and held at the corners in the "stacked and pegged" style. This method of construction was popular with French Canadian settlers, but the University Maine at Fort Kent notes this configuration had not been physically documented previously.

The Dennysville Historic District is primarily a grouping of nineteenth-century buildings, mostly residences, but includes a church, library, former academy (now museum), legion hall, and former inn. The district runs along the western shore of the Dennys River roughly two miles north of the Dennys Bay. Located in a remote part of the state, Dennysville was founded soon after the American Revolution. Early settlement was difficult, but with plentiful timber and close proximity to the river, the lumber industry began to thrive.

The Lovell Meeting House was built as the town hall and as a religious meeting place. The building was originally two stories tall, with gallery space on the second level. The symmetrical facade faces south with the entry door in the center. The building has a large window in the center of the west (street facing) elevation with a king truss (likely not an original element) in front of a carved wooden panel in the gable peak. There is simple wood-block quoining at the corners. Currently, it is a single-story wood-frame structure with a side gabled roof and clapboard siding.

Located on Lermond Pond, the Lermond Mill is comprised of two buildings. Both are timber framed with gabled roofs and wood shingle siding. The building constructed in 1803 is one-and-a-half stories. The second section was built in 1825 and is two stories. Both structures are joined by a small one-story shed with a gable roof and shingle siding. John Lermond came to Union in 1795 and built the dam that created Lermond Pond which powered a pit saw mill. By 1803 the present mill was constructed to serve as a grist mill.