The Missoula County Courthouse, designed by A.J. Gibson, Missoula's premier architect, was constructed between 1908 and 1910 and occupies an entire city block. The neoclassical sandstone block building has an integral iron-clad dome that is crowned externally by a clock tower, with clocks on all four sides. Within the tower is a two-ton bell that rings on the half hour and the hour.

The building's interior continues the classical tradition. On the main floor, a rotunda extends upward, culminating in an ornately decorated dome. The plaster columns supporting the rotunda are Doric on the basement level, Ionic on the main floor and Corinthian on the second floor.

In 1966, an annex was added to the north side of the building. The gazebo, located on the front lawn, was funded by private donations and grants. It is a replica of an original structure that stood on the east side of the Courthouse. The Missoula County Courthouse is listed on the National Register of Historic Places.

The Courthouse contains eight (8) murals by E.S. Paxson. Edgar Samuel Paxson is probably best known for his painting of Custer's Last Stand, finished in 1899. In 1906 he moved his studio to Missoula from Butte and in 1912 began a group of murals depicting early Montana history for the Missoula County Courthouse which were finished in 1914. The eight paintings can be viewed from 8:00 a.m. to 5:00 p.m., Monday through Friday.