15 ILCS 405/10.14
If a warrant drawn upon the State Treasury or any other fund held by the treasurer is returned uncashed or redeposited by the comptroller or if a warrant has been cashed but the amount for which it was drawn, or any portion thereof, is returned to the State treasury or to a separate fund held by the State Treasurer by reason of an erroneous payment or an overpayment, and the appropriation to which the warrant was charged has not lapsed, the amount so returned shall be credited to such appropriation and shall be available for expenditure, but if the appropriation to which the warrant was charged has lapsed or if the warrant was not charged to an appropriation, the amount so returned shall be credited to the fund on which the warrant was drawn and credited to the expenditure authorization to which the warrant was charged and shall be available for expenditure unless such credit or availability is otherwise prohibited by law.
When a warrant becomes void and is cancelled under Section 10.07, any money which has been set aside by the comptroller and the State Treasurer for the payment of such warrant shall escheat to the State of Illinois, and shall be paid into the Warrant Escheat Fund. Upon proper proof that any or all of the monies represented by the void warrant constituted an overpayment to which the payee was not entitled, a State agency may have those monies credited to the appropriation to which the void warrant was charged and the monies shall be available for expenditure, but if that appropriation has lapsed or if the warrant was not charged to an appropriation the monies shall be credited to the fund on which the warrant was drawn and credited to the expenditure authorization to which the warrant was charged and shall be available for expenditure unless such credit or availability is otherwise prohibited by law.
15 ILCS 405/10.14