Mo. Rev. Stat. § 82.290

In all cities having a population of over one hundred thousand inhabitants in this state, the mayor, comptroller, auditor, register, recorder of deeds, president of the board of assessors, and their deputies, are hereby authorized and required to administer, free of charge, any and all oaths in connection with the business of their offices required to be made or submitted to or before them, by any law or ordinance now in force or which may hereafter be enacted, or which they themselves may deem necessary in the discharge of their official duties.