Mo. Rev. Stat. § 51.110: Branch clerk's office, where.

In all counties in this state now containing or that may hereafter contain seventy-five thousand inhabitants or more, and where county commissions are now or may hereafter be held at more places than one, and at places other than the county seat, said commissions shall establish a branch county clerk's office at such place, where all the records and proceedings at such place shall be safely kept and preserved, and all acts done and performed at such place shall have the same force and effect as if done at the county seat.