Mo. Rev. Stat. § 483.020: Vacancy, how filled.

When any vacancy shall occur in the office of any circuit clerk so elected, by death, resignation, removal, refusal to act or otherwise, it shall be the duty of the governor in the case of an elected clerk to fill such vacancy by appointing some eligible person to said office, who shall discharge the duties thereof until the next general election, at which time a clerk 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.