40 ILCS 5/5-161
A policeman who has received a refund under this Article and who subsequently re-enters the service and serves for a period of 3 years may repay into this fund an amount equal to the refund, together with interest at the applicable rate from the date of refund to the date of repayment. If he dies in service before the expiration of the 3 year period, his widow may repay such refunds.
If repayment is not made in full, the board shall: (a) at the time of the policeman's retirement, refund to him such portion of the sum previously refunded, which he has repaid; (b) in the case of the policemen's death prior to retirement, refund to the widow such portion of the sum previously refunded, unless within 60 days after his death, the widow repays the full amount due. If there is no widow, the amount shall be refunded in accordance with this Article.
40 ILCS 5/5-161