Mo. Rev. Stat. § 341.110

There is hereby created a "Department of Plumbing and Sewer Inspection" which department shall be under the direction and supervision of a plumbing supervisor who shall be appointed by the county commission and who is charged with the duty of carrying into effect the provisions of sections 341.090 to 341.220. Such supervisor shall be at least thirty-five years of age, a resident of the county and shall have had at least ten years' experience as a licensed plumber immediately preceding his appointment and shall serve at the pleasure of the county commission.