40 ILCS 5/6-157
A fireman who was not in the fire service of the city on the day prior to the effective date, and who was in such service prior to that day and who re-enters service thereafter and before age 57 shall receive no credit for prior service and widow's prior service annuity; provided that such service before the effective date shall be included in computing service for age and service annuity and widow's annuity.
Deductions from salary and contributions by the city for age and service annuity and widow's annuity shall be made until he attains age 57.
Such fireman has a right to receive age and service annuity, from the date of his withdrawal, as of his age on such date, of the amount provided from the credits for such annuity on such date. The annuity to which his widow shall be entitled shall be fixed in accordance with the provisions of this Article relating to annuities for widows of future entrants.
40 ILCS 5/6-157