The Mahaska County Courthouse located in Oskaloosa, Iowa, United States, was built in 1886. It was individually listed on the National Register of Historic Places in 1981 as a part of the County Courthouses in Iowa Thematic Resource. In 1986 it was included as a contributing property in the Oskaloosa City Square Commercial Historic District. The courthouse is the second building the county has used for court functions and county administration.