The second courthouse in Knoxville stood out in Carl Sandburg's memory as a “poem of a building.” It had white columns in front with a massive building behind them. It looked as though it should be a temple of justice. The edifice is one of the oldest still standing in Knox County.

On July 9, 1830, the Knox County Commissioners designated John B. Gum's log cabin in Section 32 of Henderson Township as the temporary seat of justice. About six months later, the county seat was established in Knox Township. A village was platted as the county seat and named Henderson. Later the name was changed to Knoxville.

The Commissioners then erected a log courthouse of two stories. It was twenty eight feet long and twenty five wide. William Lewis constructed the building and Parnack Owen did the finishing work. The total cost was $395.43.

As more people moved into the county, there was more business at the courthouse. It soon became apparent a larger building was needed. The people of the county wanted a courthouse that was up-to-date, fully functional and beautiful enough to impress any visitors.

On March 14, 1838, a contract was let to Zelotes Cooley and Alvah Wheeler for the erection of the new building we see today. The building was completed in 1840. John Mandeville was only twenty-two years old when he designed the handsome public edifice. He followed the Greek Revival style of architecture in his design. In the late eighteenth century, Thomas Jefferson had advocated the style for government buildings. It was copied across the country for many decades thereafter.

The people of Knoxville were very proud to have the courthouse in their village. It was placed in the center of the north side of the large public square. It was a two story brick structure which contained six rooms and a hall. The bricks were made nearby. At the last minute, the county commissioners decided to ornament the roof with a cupola. It added $725 to the cost of the building.

The courthouse cost $16,175 to erect (that is equal to more than $378,000 in today's money). It was used until 1873. The county seat was moved to Galesburg by means of political manipulation. In Galesburg, various temporary arrangements were made to house the courts and other county offices. The building where court was held burned down in 1883. A new courthouse in the city was not completed until 1886.

After the county seat had been moved to Galesburg, the former courthouse in Knoxville was used a an opera house and for public meetings. Today, the upper floor is a museum containing a variety of historical farm machinery and artifacts from Knoxville and Knox County history. New courtroom furnishings made of poplar wood have been added recently. It appears as it may have during the time Stephen A. Douglas and other early lawyers practiced there in the 1840s and 1850s.