In 1891, only three years after H. H. Richardson's Allegheny County Courthouse (
AL1) was completed, Kauffman and Butz designed the third Fayette County Courthouse. As a student at the Massachusetts Institute of Technology from 1879 to 1881, William Kauffman (1857–1945) was familiar with Richardson's work, as evidenced by his other building in Uniontown (
FA4). Edward M. Butz (1851–1916), active in Pittsburgh's German community since the 1870s, would have witnessed the construction of the Allegheny County courthouse. The architects created what architectural historian James D. Van Trump described (in his papers at the Pittsburgh History and Landmarks Foundation) as “the Allegheny County courthouse … disassembled and rearranged in a smaller version.” Uniontown's courthouse differs from Richardson's in its asymmetrical plan, its use of yellow-gray sandstone rather than pink granite, and the elimination of a lobby space; the last of these was a suggestion made in 1884 by Judge Thomas Mellon to the Allegheny County commissioners not to provide space “for loafers and hangers on.” Uniontown's small lobby only provides space for access to the stairways. It is illuminated by a stained glass dome. Murals in the upper lobby were painted by Ohio artist Alice Schille (1869–1955) in 1905. Courtroom No. 1 retains most of its original fittings, but the other major courtroom has been altered. The “bridge of sighs” connecting the jail to courtroom No. 1 was added in 1902. It is uncertain whether its design was provided by the same architects.

A four-story Italian Renaissance Revival county office building designed by Emil R. Johnson and Clarence F. Wilson was added to the east in 1927–1928. Its central section echoes the courthouse's triple-arched entrance, which is topped by a row of arched windows. Set into the smooth limestone walls above the entrance are stone relief panels commemorating agriculture and coal mining, Fayette County's two main industries.