Mo. Rev. Stat. § 143.511

Income tax returns required by sections 143.011 to 143.996 shall be filed on or before the fifteenth day of the fourth month following the close of the taxpayer's taxable year except where the taxpayer is an exempt organization. Exempt organizations shall have the same due date as set by the Internal Revenue Code of 1986, as amended. A person required to make and file a return under sections 143.011 to 143.996 shall, without assessment, notice, or demand, pay any tax due thereon to the director of revenue on or before the date fixed for filing such return (determined without regard to any extension of time for filing the return). The director of revenue shall prescribe by regulation the place for filing any return, declaration, statement, or other document required pursuant to this chapter and for the payment of any tax.