Mo. Rev. Stat. § 57.080
Whenever from any cause the office of sheriff becomes vacant, the same shall be filled by the county commission; if such vacancy happens more than nine months prior to the time of holding a general election, such county commission shall immediately order a special election to fill the same, and the person by it appointed shall hold said office until the person chosen at such election shall be duly qualified; otherwise the person appointed by such county commission shall hold office until the person chosen at such general election shall be duly qualified; but while such vacancy continues, any writ or process directed to the said sheriff and in such sheriff's hands at the time such vacancy occurs, remaining unexecuted, and any writ or process issued after such vacancy, may be served by any person selected by the plaintiff, the plaintiff's agent or attorney, at the risk of such plaintiff; and the clerk of any court out of which such writ or process shall issue shall endorse on such writ or process the authority to such person to execute and return the same, and shall state on such endorsement that the authority thus given is "at the request and risk of the plaintiff", and the person so named in said writ or process may proceed to execute and return said process, as sheriffs are by the law required to do. Such election shall be held on or before the tenth Tuesday after the vacancy occurs. Upon the occurrence of such vacancy, it shall be the duty of the presiding commissioner of the county commission, if such commission be not then in session, to call a special term thereof, and cause said election to be held.
§ 57.080, RSMo
RSMo 1939 § 13143, A.L. 1978 H.B. 971, A.L. 1979 S.B. 275, A.L. 1996 H.B. 1557 & 1489, A.L. 2005 S.B. 176, A.L. 2010 H.B. 1516 Revision merged with H.B. 1965