The first courthouse was a wood frame two-story building erected during 1846–1848. The second Marion County Courthouse was designed by D. H. Young and was built in 1858. That courthouse was one of Iowa's outstanding examples of the Greek Revival mode. All of the walls of that two-story brick building were articulated with wide pilasters reaching
The architect Mifflin E. Bell of Chicago selected the popular Richardsonian Romanesque for the third courthouse. The structure is three stories tall, plus an attic. The central tower, with arched openings for the bells and the heavy round corner buttress of its base, is a particularly strong example of the style. The architectural treatment of the body of the building and its roof carries one over just a bit into the French Châteauesque style. Some restoration of the building took place in 1968.