40 ILCS 5/15-148
The survivors annuity is payable monthly. Any annuity due but unpaid upon the death of the annuitant, shall be paid to the annuitant's estate.
A person who becomes entitled to more than one survivors insurance benefit because of the death of 2 or more persons shall receive only the largest of the benefits; except that this limitation does not apply to a survivors insurance beneficiary who is entitled to a survivor's annuity by reason of a mental or physical disability.
A survivors insurance beneficiary or the personal representative of the estate of a deceased survivors insurance beneficiary or the personal representative of a survivors insurance beneficiary who is under a legal disability may waive the right to receive survivorship benefits, provided written notice of the waiver is given by the beneficiary or representative to the board within 6 months after the death of the participant or annuitant and before any payment is made pursuant to an application filed by such person.
40 ILCS 5/15-148