40 ILCS 5/12-133.2
Employees who retired on service retirement annuity prior to July 1, 1965 who were at least 55 years of age at date of retirement and had at least 20 years of credited service, who shall have attained age 65, and any employee retired on or after such date who meets such qualifying conditions and who is not eligible for an annual increase in basic retirement annuity otherwise provided in this Article, shall be entitled to receive benefits under this Section.
These benefits shall be in an amount equal to 1 1/2% of the service retirement annuity multiplied by the number of full years that the annuitant was in receipt of such annuity. This payment shall begin in January of 1970, and an additional 1 1/2% based upon the original grant of annuity shall be added in January of each year thereafter. Beginning January 1, 1972, the annual rate of increase in annuity shall be 2% of the original grant of annuity and shall also apply thereafter to any person who shall have had at least 15 years of credited service and less than 20 years on the same basis as was applicable to persons retired with 20 or more years of service; provided that beginning January 1, 1976, the annual rate of increase in retirement annuity shall be 3% of the basic retirement annuity.
An employee annuitant who otherwise qualifies for the aforesaid benefit shall make a one-time contribution of 1% of the final monthly average salary multiplied by the number of completed years of service forming the basis of his service retirement annuity, provided that if the annuity was computed on any other basis, the contribution shall be 1% of the rate of monthly salary in effect on the date of retirement multiplied by the number of completed years of service forming the basis of his service retirement annuity.
40 ILCS 5/12-133.2