Mo. Rev. Stat. § 55.050: Term of office — vacancy, how filled (second class and certain first class counties).

At the general election in the year 1946, and every four years thereafter, a county auditor shall be elected in each county of the first class not having a charter form of government and in each county of the second class. He shall be commissioned by the governor and shall enter upon the discharge of his duties on the first Monday in January next ensuing his election. He shall hold his office for the term of four years and until his successor is duly elected and qualified, unless he is sooner removed from office. If a vacancy occurs in the office by death, resignation, removal, refusal to act, or otherwise, the governor shall fill the vacancy by appointing some eligible person to the office, who shall discharge the duties thereof until the next general election, at which time an auditor shall be chosen for the remainder of the term, who shall hold his office until his successor is duly elected and qualified, unless sooner removed.