Mo. Rev. Stat. § 86.353
The right of any person to a benefit, any other right accrued or accruing to any person under the provisions of sections 86.200 to 86.366 and the moneys created pursuant to sections 86.200 to 86.366 are not subject to execution, garnishment, attachment or any other process whatsoever and are unassignable except as in sections 86.200 to 86.366 specifically provided. Notwithstanding the foregoing, nothing in this section shall prevent the board of trustees from honoring the terms of a court order requiring the retirement system to pay all or any portion of the retirement benefit otherwise payable to a retired or disabled member to a third party to satisfy the member's obligation to pay child support or maintenance. Any relief association created pursuant to section 86.500 shall be exempt from the tax imposed by sections 143.011 to 143.1013.
§ 86.353, RSMo