The U.S. Custom House is a skillful blend of the Renaissance Revival and Second Empire styles, which were popular in the United States during the mid- to late 19th century.
Its original design is largely intact.
The three-story, free-standing, I-shaped structure is constructed of New Hampshire granite with a slate-shingled hipped roof.
These fireproof materials were chosen in response to the 1866 fire.

The building rests on a sloping lot that forms an embankment along the sides and the Fore Street entrance of the building.
A heavy cast-iron railing, designed of tangent ovals, rests on top of the embankment.
The basement level is accented with a rusticated granite exterior finish.

The U.S. Custom House has a shallow I-shaped plan, with projecting pedimented entry pavilions on the Fore Street and Commercial Street facades.
The entire building is dominated by large and handsome rhythmic, round-headed windows with simple keystones.
The window openings are flanked by engaged Doric columns on the first and second stories.
Square pilasters mark the corners of the pavilions and the facades.
A cornice and balustrade surround the entire building.
The cornice features ornamental triglyphs (three vertical bands separated by V-shaped grooves).

Distinctive twin, square cupolas rise above the pedimented pavilions.
Double Corinthian order pilasters flank arched Venetian windows, each of which is capped with a shallow pediment.
The cupolas' distinctive mansard roofs are a defining feature of the Second Empire style.

The building is organized around the grand two-story customs hall, which is the building's public showplace and occupies the central portions of the first and second floors.
The marble floor of the hall is laid with a sophisticated checkerboard pattern.
Two counters run the length of the room and are fashioned of several different types of marble that were quarried on an island in Lake Champlain.
These include a dark veined marble for the base; a red variegated marble for the pilasters, cornice and panels; a jet-black marble for the beading around the panels; and a dove-gray marble for the counters.
Encircling the hall at the second floor is a narrow gallery with a decorative iron rail.
The gallery is ornamented with symbols relating to commerce in the United States, including corn and tobacco leaf motifs and dolphins flanked by oak and olive leaves.

The ceiling of the customs hall is highly ornamented.
A large plaster cove rises from the second-floor openings to an elaborate plaster cornice and coffered ceiling.
Groin (cross) vaults over each second floor-opening extend from the cove, and the ceiling beams are decorated with a Greek key pattern and bosses (elaborate joints) at beam intersections.

An eight-foot, walnut, pedestal-mounted counter capped with a spherical clock stands at the center of the customs hall.
The counter contains an octagonal writing surface decorated with flutes, bosses, a collar, and modified Ionic order scrolls.

The original walnut woodwork is still intact throughout the building, as are the Italian marble fireplaces in the offices located at both ends of the building.
The offices, which are more simply designed than the main hall, consist of plaster walls, and walnut baseboards, window surrounds, and doors.
The original 2 story vault for storing valuables also remains.

The U.S. Custom House has experienced only minor changes since it was constructed, and therefore exhibits a high degree of architectural integrity.
The most notable alteration to the structure has occurred in the interior customs hall, where the original gas chandeliers have been replaced with the current surface-mounted ceiling fixtures.
The basement was converted into office and dormitory space for the U.S. Coast Guard in 1983.
The majority of the building's distinctive elements, such as the marbled checkerboard floor and decorative staircases, remain in place.
In 1998, the aluminum doors, which were installed during the 1960s at the main entrances, were replaced with wooden doors similar in design and color to the original doors to
The U.S. Custom House is a skillful blend of the Renaissance Revival and Second Empire styles, which were popular in the United States during the mid- to late 19th century. Its original design is largely intact. The three-story, free-standing, I-shaped structure is constructed of New Hampshire granite with a slate-shingled hipped roof. These fireproof materials were chosen in response to the 1866 fire.
The building rests on a sloping lot that forms an embankment along the sides and the Fore Street entrance of the building. A heavy cast-iron railing, designed of tangent ovals, rests on top of the embankment. The basement level is accented with a rusticated granite exterior finish.
The U.S. Custom House has a shallow I-shaped plan, with projecting pedimented entry pavilions on the Fore Street and Commercial Street facades. The entire building is dominated by large and handsome rhythmic, round-headed windows with simple keystones. The window openings are flanked by engaged Doric columns on the first and second stories. Square pilasters mark the corners of the pavilions and the facades. A cornice and balustrade surround the entire building. The cornice features ornamental triglyphs (three vertical bands separated by V-shaped grooves).
Distinctive twin, square cupolas rise above the pedimented pavilions. Double Corinthian order pilasters flank arched Venetian windows, each of which is capped with a shallow pediment. The cupolas' distinctive mansard roofs are a defining feature of the Second Empire style.
The building is organized around the grand two-story customs hall, which is the building's public showplace and occupies the central portions of the first and second floors. The marble floor of the hall is laid with a sophisticated checkerboard pattern. Two counters run the length of the room and are fashioned of several different types of marble that were quarried on an island in Lake Champlain. These include a dark veined marble for the base; a red variegated marble for the pilasters, cornice and panels; a jet-black marble for the beading around the panels; and a dove-gray marble for the counters. Encircling the hall at the second floor is a narrow gallery with a decorative iron rail. The gallery is ornamented with symbols relating to commerce in the United States, including corn and tobacco leaf motifs and dolphins flanked by oak and olive leaves.
The ceiling of the customs hall is highly ornamented. A large plaster cove rises from the second-floor openings to an elaborate plaster cornice and coffered ceiling. Groin (cross) vaults over each second floor-opening extend from the cove, and the ceiling beams are decorated with a Greek key pattern and bosses (elaborate joints) at beam intersections.
An eight-foot, walnut, pedestal-mounted counter capped with a spherical clock stands at the center of the customs hall. The counter contains an octagonal writing surface decorated with flutes, bosses, a collar, and modified Ionic order scrolls.
The original walnut woodwork is still intact throughout the building, as are the Italian marble fireplaces in the offices located at both ends of the building. The offices, which are more simply designed than the main hall, consist of plaster walls, and walnut baseboards, window surrounds, and doors. The original 2 story vault for storing valuables also remains.
The U.S. Custom House has experienced only minor changes since it was constructed, and therefore exhibits a high degree of architectural integrity. The most notable alteration to the structure has occurred in the interior customs hall, where the original gas chandeliers have been replaced with the current surface-mounted ceiling fixtures. The basement was converted into office and dormitory space for the U.S. Coast Guard in 1983. The majority of the building's distinctive elements, such as the marbled checkerboard floor and decorative staircases, remain in place. In 1998, the aluminum doors, which were installed during the 1960s at the main entrances, were replaced with wooden doors similar in design and color to the original doors to
United States Custom House (Portland, Maine)