Mo. Rev. Stat. § 58.020

At the general election in the year 1948, and every four years thereafter, the qualified electors of the county at large in each county in this state in which a coroner is to be elected shall elect a coroner who shall be commissioned by the governor, and who shall hold his office for a term of four years and until his successor is duly elected or appointed and qualified. Each coroner shall enter upon the duties of his office on the first day of January next after his election.