Mo. Rev. Stat. § 55.010
In all counties of the first class having a charter form of government there shall be a county auditor who is the budget officer and accounting officer of the county and who shall perform all the duties imposed by the county budget law upon the budget officer and accounting officer. The county commission shall appoint and fix the compensation of some competent person as county auditor, who shall serve for a term of four years from and after the first day of January, 1947, and until his successor is duly appointed and qualified. In case of a vacancy in the office of county auditor caused by death, resignation or otherwise, the county commission shall appoint some qualified person for the unexpired term of the county auditor. The county commission shall employ and fix the compensation of clerical and other assistants to the county auditor necessary to enable him to efficiently perform his duties.
§ 55.010, RSMo