Mo. Rev. Stat. § 86.013
In all cities of this state that now have or may hereafter attain a population of five hundred thousand or more, there are hereby created and established retirement or pension systems for the purpose of providing retirement allowances for policemen of such cities; except that, any city which establishes a police retirement system under any other provisions of this chapter prior to attaining a population of five hundred thousand or more, may elect to continue its police retirement system under such other provisions of this chapter, and the provisions of sections 86.010 to 86.193 shall not apply to any city which makes such election. Each such system shall be under the management of a board of trustees herein described and shall be known as "The Police Retirement System of ______ (name of city)" and by such name all of its business shall be transacted, all of its funds invested, and all of its cash and securities and other property held. The retirement systems so created shall begin operation as of the first day of October, 1929.
§ 86.013, RSMo