40 ILCS 5/6-196
The following amounts shall be credited to this reserve: (1) Amounts deducted from salaries of firemen for age and service annuity and widow's annuity; (2) amounts contributed by the city for any such annuity purpose for any fireman who receives duty disability benefit, in lieu of deductions from his salary; and (3) amounts transferred to this reserve from the investment and interest reserve.
An individual account shall be kept for each fireman from whose salary any such amount is deducted. As such amounts are received, they shall be allocated and credited to the respective accounts of the firemen.
At least once each year, and always before any moneys shall be transferred to any other reserve, the sums credited shall be improved by interest.
When the annuity for a fireman or widow is fixed or granted, the total amount in this reserve for the purpose of the annuity and required therefor shall be charged thereto and credited to the annuity payment reserve.
Amounts resulting from salary deductions, and amounts resulting from contributions of the city for any fireman who receives duty disability benefit in lieu of deductions from his salary, that are to be refunded in accordance with the provisions of this Article, except those referred to in Section 6-197, shall be charged to this reserve.
40 ILCS 5/6-196