Hartford's Municipal Building, the seat of City government, was dedicated and opened on November 4, 1915. It replaced the Old State House as the City Hall. It was named the Municipal Building because it was originally intended that the City would continue to use the Old State House and, in the public mind, that building was "City Hall".

        A portion of the land on which the Municipal Building was constructed was donated by J. Pierpont Morgan, a Hartford native and well-known financier. J.P. Morgan had given land to the Wadsworth Atheneum for construction of an addition to the museum, the Morgan Memorial. He became concerned that the land directly south of the Morgan Memorial might be developed in a manner unsympathetic to the museum. He, therefore, made it possible for the Atheneum to acquire 2/3 of the land and give it to the City "for some worthy municipal building or for a public square". The remainder of the parcel was purchased by the City.

        Planning for the new Municipal Building began in 1911 and was overseen by John M. Carrere, architectural consultant to the City, who had attended the Ecole des Beaux-Arts in Paris. Concept plans were developed by the architectural firm of Brocklesby and Smith which set the style and general scheme for the new building. A formal competition was held and the rules of the competition stated that only the Beaux-Arts style (then called Georgian) was acceptable, that the new building must be compatible with Hartford's architectural heritage (in particular, the Old State House) and must harmonize in scale and character with its nearest neighbor, the Morgan Memorial.

        The Municipal Building was constructed in two parts (east and west) by two different construction companies. This was done because there were not sufficient funds available to enter into a contract for construction of the entire building. The City had appropriated $300,000 in 1910 for construction of a small building to house government offices. With these funds, the City contracted with Norcross Brothers of Worcester, Massachusetts to construct the Main Street "pavilion", the portion of the building which is west of the atrium.

        The cornerstone was laid on July 9, 1912. Later that year an additional $1.1 million was appropriated for the remainder of the structure and P. Carlin Construction Company of New York was hired to do the work. The only visible indication of where the two parts were joined is a row of half tiles in front of the second story atrium floor. The total cost of the building was $1,788,000, including the furnishings and architectural fees.

        The building is constructed of brick and faced with white Bethel granite. There is very little wood in the building. In 1910, the Court of Common Council directed that the new building should be as "fireproof as possible". Wood is found primarily in the doorframes and doors (which are mahogany) and the wainscoting in the Function Room and former Probate Court, not in the structural materials of walls or floors. The floors of the building are carried on steel beams and terra cotta arches and the roof is constructed of copper and tile, all fireproof materials.

        At the time it was built, the Municipal Building covered a full city block between Main, Arch, and Prospect Streets and the former Atheneum Street South which ran along the north side of the building. In 1969, Atheneum Street South was closed and Burr Memorial Mall created.

        There are four entrances to the Municipal Building on two different levels. The west entrance, from Main Street, and the north entrance, from Burr Mall, enter between the ground and first floors. The south door, from Arch Street, and the east entrance, from Prospect Street, enter on the ground floor level. All of the entrances are bronze and contain revolving doors.

        In 1979, the Municipal Building was nominated for inclusion on the National Register of Historic Places and was officially accepted in 1981.