Mo. Rev. Stat. § 54.033: County treasurer vacancy caused by death, interim treasurer appointed, how.

In the event of a vacancy caused by death, resignation, or otherwise, in the office of county treasurer in any county except a county having a township form of government with an office of collector-treasurer and any county with a charter form of government, the county commission shall appoint a deputy treasurer or a qualified person to serve as an interim treasurer until said treasurer returns or the unexpired term is filled under section 105.030. Such individual must be eligible to serve as a county treasurer under section 54.040, and must comply with section 54.090.