English: Built in 1839, 1851, and 1864, this Greek Revival-style building was designed by Henry Singleton, and was later renovated by Robert S. Mitchell and William Rumbold, adding several of the building’s wings and present features. The oldest section of the courthouse is the foundation of the east wing, which extends towards the Mississippi River, and is the only remaining portion of the 1816-1828 Federal-style courthouse that stood on the same site, which was designed by the firm Laveille and Morton, and was incorporated into the larger present courthouse structure in 1839, before being removed and replaced with the present east wing during the 1851 renovation. The 1839 portion of the building, designed by Henry Singleton, consists of the north, south, and west wings, which once surrounded a rotunda with a low dome, much like the original design of the United States Capitol. In 1851, under the direction of architect Robert S. Mitchell, the east wing was removed and replaced with the present structure, with the new east wing better matching the 1839 wings. In 1861-1864, under the direction of architect William Rumbold, a cast iron dome, based on St. Peter’s Basilica in Rome, and similar to the dome on the United States Capitol, was added to the center of the building, at which time the building took on its present form. Upon the addition of the dome, the courthouse was the tallest building in St. Louis and Missouri until 1896, when St. Louis Union Station was constructed. In addition to its architectural history, in the 1850s, the courthouse was where the Dred Scott Case was heard, prior to the case being brought before the US Supreme Court, and slave auctions were regularly held inside the Probate Courts chambers in the building’s east wing, where slaves owned by deceased slaveholders without a hard will, and slaveowners who had declared bankruptcy, were sold. This practice ended in 1861. The building continued to serve as the St. Louis County Courthouse until St. Louis City split from St. Louis County in 1877, and subsequently served as the St. Louis City Courthouse until 1930, when the present City Courts building was completed seven blocks to the west.

The building features a stone exterior with doric pilasters, two-story porticoes on the north, east, and west wings with fluted doric columns and pediments, gabled roofs with pediments, architraves with triglyphs and recessed panels, six-over-six double-hung windows, a central dome on an octagonal base with engaged doric columns and arched windows on the lower portion of the drum, a cornice below oxeye windows and a copper-clad dome above, a lantern with a decorative balustrade at the base, arched bays, and doric columns, with a domed roof and flagpole at the top. Inside, the building features many well-preserved historic spaces that operate as a museum, including a rotunda with murals by artist Karl Ferdinand Wimar, fluted corinthian pilasters with gilded capitals, doric, ionic, and corinthian columns, historic chandeliers, arced staircases, coffered ceilings, marble floors, wooden furniture, wooden paneled doors, and wooden paneling.

The building is part of the Jefferson National Expansion Memorial, listed on the National Register of Historic Places in 1966. Since the mid-20th Century, the building has functioned as a museum, interpreting the history of the building and the surrounding city, which became part of the Jefferson National Expansion Memorial in 1940, and Gateway Arch National Park, upon re-designation of the national memorial in 2018. As of 2023, the courthouse is undergoing an extensive renovation, which will make the building accessible to those with physical disabilities and limitations, replace building systems, modernize National Park Service office spaces in the building, update galleries and exhibits, and restore the historic features of the building.