Mo. Rev. Stat. § 137.495
Every person, corporation, partnership or association subject to taxation pursuant to the laws of this state and owning or controlling tangible personal property taxable by the cities shall file with the assessor of the cities a return listing all such tangible personal property so owned or controlled on January first of each year and estimating the true value thereof in money. The return shall be filed between the first day of January and the first day of April of each year, shall be signed by the taxpayer, and shall be certified by the taxpayer as being a true and complete list and statement of all the tangible personal property and the estimated value thereof. If the first day of April is a Saturday or Sunday, the last day for filing shall be the next business day.
§ 137.495, RSMo