The new United States Customhouse and Post Office was opened for public inspection on June 23, 1894, and was visited by approximately 5,000 citizens during the day and evening. It was built on Boonville Avenue between Pine and Central Streets. It sits on what is now the Chestnut Expressway.

The entire structure is made of limestone in the Richardsonian Romanesque style of architecture, characterized by round arches and vaults. It contains towering stone turrets and gargoyle waterspouts. The south wing is topped with a turret and tower from which National Weather Bureau flags were flown. The site was chosen after fierce dialog between the northsiders and southsiders about where the city should locate the structure. The northsiders won, with their site being chosen over a site at the corner of St. Louis and Jefferson.

The entire first floor of the building was the United States Post Office, with the postmaster's business office in the southeast corner. The first floor is made entirely of marble. The office of the internal revenue collector was immediately in front of the second floor landing. The opposite side of the second floor contained the office of the local weather observer. The United States land office occupied rooms six, seven and eight on the second floor. The land records were kept in a fire-proof vault on the second floor. The United States marshal, the district attorney and a witness room completed the second floor.

The third floor contained the courtroom, which the Democrat (newspaper) describes as having too small a capacity to allow for the crowds lured by interesting cases. The court library and court offices also make up the third floor.

The "government building", as it was called, was remodeled and enlarged in 1914 and the photograph on the second postcard was obviously taken after this because it shows an area on the back (northwest) side of the building, which is not there in the earlier postcard. The small turret was also removed from the northwest corner of the building when the expansion was made.

On May 16, 1922, a fire broke out in a storeroom of the Weather Bureau, causing $35,000 in damage. Walls and furniture on all three floors were damaged.

The building served the United States government until 1938. In that year a new federal building directly north of the old site was built. The post office, federal courts and other government offices moved into the new Federal Building and the city obtained the old building, renamed City Hall. The first City Council meeting was held on October 10, 1938, just one day after it became City Hall.