Mills county was organized in 1851. The county seat was located at Glenwood, which was called Coonville at the time. The first courthouse was built in 1857 and was two stories high with the courtroom on the second floor. The building was made of brick with a tin roof. There is evidence that it cost between $25,000 and $40,000 to build.
After serving the county for over 100 years, the old courthouse was replaced. The second courthouse was started in 1958 and completed in 1959 for a total cost of $319,038.09. This courthouse currently serves Mills County.