Mo. Rev. Stat. § 49.520

Whenever the governing body of any first class county finds it necessary for the public need or convenience, or for the preservation of the public records to build, repair or remodel a courthouse, office buildings, court buildings or other public buildings in the county or to purchase, construct or extend buildings and the land upon which the buildings are situated, to be used by the county for courthouses or other proper county purposes, the county is authorized and empowered to purchase, construct or extend courthouses, office buildings, court buildings, and other buildings used for county purposes upon its own land or to acquire by purchase the land upon which the buildings are to be built.