Mo. Rev. Stat. § 66.351

For the purpose of distributing taxes under the provisions of Section 30(a) of Article IV of the State Constitution and sections 66.350 and 66.620, the results of any federal decennial census shall not be considered final when initially certified by the United States government to the director of revenue. If such initial certification is received by the director prior to the first day of July, the census results shall be used for distributions made on or after January first of the next year. If such initial certification is received on or after the first day of July, the census results shall be used for distributions made on or after July first of the next year.