Missouri Revised Statutes Title XXXVIII. Crimes and Punishment; Peace Officers and Public Defenders § 590.020. Peace officer license required, when--classes of officers established--no license required, when

(1) Of any person who has no power of arrest;

(2) To seek or hold an elected county office, subject to such requirements as chapter 57 may impose;

(3) To be commissioned pursuant to section 64.335 as a park ranger not carrying a firearm;

(4) To be commissioned as a peace officer by a political subdivision having less than four full-time paid peace officers or a population less than two thousand, provided that such commission was in effect on August 28, 2001, and continually since that date, and provided that this exception shall not apply to any commission within a county of the first class having a charter form of government;

(5) Of any reserve officer continually holding the same commission since August 15, 1988; or

(6) For any person continually holding any commission as a full-time peace officer since December 31, 1978.