Originally known as the United States Custom House and Post Office, the Old Post Office in St. Louis, Missouri was also a courthouse built between 1873 and 1884. It was one and the only surviving of the five grand federal buildings ordered to be constructed in New York, Boston, Philadelphia, Cincinnati, and St. Louis when the Civil War ended in 1865 to serve as a psychological motivation and to instill confidence and pride in the government. It opened in 1884 and was the main channel of communication for commerce and to and from all points west with hundreds of millions of mails handled just the first year alone. The Old Post Office was also home to several federal offices administering the post-Civil War expansion westward, the Eighth Circuit federal court (which grew to be the largest circuit in the nation by 1891) and the United States District Court for the Eastern District of Missouri, which both met here until 1935.

The architectural design of the building was considered as French Second Empire also referred to as the ?General Grant Style? because it was popularized during his term as president of the United States from 1869 to 1877. The fa?ade of the first floor was put together with Iron Mountain Red Granite while the frontage of the upper three levels (including the floors housing the Court of Appeals) is made of Grey Hurricane Island Granite from Maine. On the lower part of the dome, Daniel Chester French sculpted a masterpiece entitled ?Peace and Vigilance? also called "America at War and America at Peace". A replica of the sculpture replaced the original work which was restored and moved to the first floor of the building.

Innovative systems for heating and ventilation were incorporated in the design that also allowed brilliant use of natural light in the Old Post Office. With fireproofing as the most important aspect of the design, the entire framework of the building and dome, as well as stairwells, doorjambs and window frames were all rendered in cast iron which also made the intense decorative detailing more affordable than hand carving. Other remarkable interior features are ornamental plaster cornices and medallions, art glass windows, bronze doorknobs displaying the Seal of the United States, cast-iron ventilation grilles, red Italian Bologna marble mantels and wall-to-wall tapestries of encaustic tile adorning the third and fourth floors and two grand stairwells.

The Old Post Office, a National Historic Landmark, continues to operate as a mixed-use facility serving federal and private purposes like hosting the downtown campus for Webster University. When it was owned by the United States General Services Administration (GSA), the Old Post Office was categorized as the sixth most historic and the seventh most architecturally significant building out of the over 2200 buildings the GSA owned. The Courtroom and Library in the Old Post Office are designated ?Level 1?, a classification bestowed for only the most historically significant structures, such as the Statue of Liberty, the Old Courthouse in St. Louis, and the Rotunda in Washington, D.C.