The construction began in 1838 on the historic Johnson Courthouse. It is a two-story red brick Federal-style building which faces Main Street. The courthouse anchored the area and soon saw the construction of several businesses. In 1842 at the intersection of Main and West Gay Street, the city's first masonry store was constructed. The area around the courthouse came to be known as Old Town Warrensburg.
In 1850 the population of Warrensburg was 241 and in 1855 the Missouri Legislature incorporated Warrensburg as a town. The small community continued to develop and spread east and by 1860 the population had risen to 982. The local economy was primarily agriculturally based, and Warrensburg was on its way to becoming an important center for buying and selling the county's agricultural products.