Mo. Rev. Stat. § 483.010: Qualifications of a clerk.

No person shall be appointed or elected clerk of any court, unless he be a citizen of the United States, above the age of twenty-one years, and shall have resided within the state one whole year, and within the geographical area over which the court has jurisdiction or, in the case of circuit clerks, within the county from which elected, three months before the appointment or election; and every clerk shall, after his appointment or election, reside in the geographical area over which the court he serves has jurisdiction or, in the case of circuit clerks, in the county for which he is clerk.