Mo. Rev. Stat. § 57.570

The sheriff in all counties of class one now or hereafter having more than five hundred thousand inhabitants and not having a charter form of government, with the approval of the county commission, may create a force consisting of a superintendent and other officers, sergeants, patrolmen and radio personnel to be known as the county highway patrol. The sheriff shall prescribe rules for instruction and discipline, make all administrative rules and regulations and fix the hours of duty for members of the patrol.