Mo. Rev. Stat. § 58.040: Vacancy filled by governor.

When any vacancy shall occur in the office of coroner by death, resignation, removal, refusal to act, or in any other manner, it shall be the duty of the governor to fill such vacancy by appointing some eligible person to such office. The person so appointed shall take the oath, give bond and otherwise qualify for the office as required of coroners regularly elected, and shall discharge the duties of such office for the remainder of the term for which he is appointed.