Mo. Rev. Stat. § 82.170

Nothing in this chapter contained shall be construed to limit or abridge the term of office which any representative in the municipal legislature of such city shall be elected to fill, but every such representative shall be deemed and taken, for the residue of the term for which he may have been elected, a representative of that ward in which his actual residence and place of abode may be at the time of any division of such city into wards, creation of any new ward or wards, or change in the boundaries of any ward or wards.