Mo. Rev. Stat. § 221.320
In each county of the state the presiding judge of the circuit court, or such other judge or judges as may be determined by local circuit court rule, may, upon the petition of fifteen reputable citizens or upon the motion of a majority of the court en banc, appoint six persons, three of whom shall be women, and not more than three shall have the same political affiliations, who shall constitute a board of county visitors, all of whom, upon the fixed appointment, shall serve for one year and shall constitute the board of visitors for the inspection of all corrective institutions supported by such county. The members of the board shall serve without compensation and shall enjoy the same immunity from lawsuits as judicial officers.
§ 221.320, RSMo