Mo. Rev. Stat. § 182.480
As of October 13, 1965, and any other provisions of law to the contrary notwithstanding, all of the area or territory included within the geographical boundaries of a city, including any area or territory which becomes a part of any city pursuant to any annexation pending on October 13, 1965, which maintains a free public library supported at least in part by taxation, shall be a "municipal library district" and shall have as its purpose the furnishing of free public library services to residents of the district, and the district shall be known as "The city of ______ Municipal Library District", and each such district shall be a political subdivision of the state of Missouri and a body corporate with all the powers and rights of like or similar corporations, and as of the effective date of sections 182.130 and 182.480 to 182.510, all of the area or territory which is hereby included within a municipal library district shall be excluded from the boundaries of any existing county library district, and all of the taxable property located in the municipal library district shall only be subject to taxation by the municipal library district and shall hereafter not be subject to taxation by the county library district; provided, however, that after October 13, 1965, any annexation by a city having within its boundaries a municipal library district shall not extend the boundaries of the municipal library district, and any annexed areas shall remain in the county library district, and the taxable property in any such annexed areas shall only be subject to taxation by the county library district and shall not be subject to taxation by the municipal library district; except, that in any county not having a county library any such annexation shall likewise extend the boundaries of any existing municipal library district.
§ 182.480, RSMo