Mo. Rev. Stat. § 58.010

In each county of the state, except in counties of the second class which prior to January 1, 1975, have a population of more than one hundred twenty thousand and less than two hundred thousand, and counties of the first class not having a charter form of government and any other county which adopts the provisions of sections 58.700 through 58.765, there shall be an office of coroner.