The first courthouse was built during the winter of 1844-1845. Settlers raised the timbers that were to serve as the superstructure for the two-story frame courthouse. When finished, it measured 28 by 50 feet, and served as the courtroom, church, and opera house. The courtroom was not used by the county after 1855.
Office space was rented in various parts of town until the present courthouse was built. This courthouse is over three stories high and is made of brick which rests upon a stone foundation. It is built on what used to be the north half of the east side of the Oskaloosa public park. The building, which cost the county $132,500, was dedicated in 1886. A bronze statue of Chief Mahaska faces west on the courthouse grounds to symbolize the spirit of the pioneer.