Mo. Rev. Stat. § 48.050: Effect of change of class on county offices and officers.

Any elected county official whose office may be abolished or consolidated with another office as a result of the change of the county from one class to another shall continue to hold the office to which he was elected for the term for which he was elected. Any office which may be established as a result of the change of the county from one class to another shall be filled in accordance with the provisions of the law relating to the filling of vacancies for such office.