The Monona County Courthouse in Onawa in western Iowa dates to 1892, when construction was completed on the brick building with stone trim. The Richardson Romanesque building was designed by S.E. Maxon, who also designed the courthouse in Greenfield in Adair. The building saw additions in 1967 and 1973, along with the construction of an annex in 1981 for additional court and human services facilities. The Monona County Courthouse was added to the National Register of Historic Places in 1981.