Mo. Rev. Stat. § 542.190
Current with changes from the 2023 Legislative Session
No sheriff of a county, mayor of a city or other private person authorized by law to appoint special deputies, marshals or policemen in this state to preserve the public peace and quell public disturbances shall appoint as special deputies, marshals or policemen any person who is not a resident of this state and who has not been a resident of this state for at least three years prior to his appointment.
§ 542.190, RSMo
RSMo 1939 § 4622, A.L. 1955 p. 515