40 ILCS 5/12-146
When any person receiving an annuity shall re-enter service, the annuity previously granted to such person and any annuity fixed for his wife shall be cancelled. Such employee shall be credited, in accordance with the applicable actuarial tables, with sums sufficient to provide annuities equal in amount to those cancelled for the employee and wife, as of their respective ages on the date of the employee's re-entrance into service. Employee Contributions as salary deductions shall be made from the time of such re-entry into service. Upon subsequent retirement, new annuities based upon the amounts to the credit of the employee for annuity purposes, and the entire period of his service, shall be fixed for the employee and his wife.
In the case of an employee described in the foregoing paragraph, whose wife for whom annuity was fixed prior to such re-entry died before he re-entered service, any sum to the credit of the employee for widow's service annuity and widow's prior service annuity at the time annuity for such wife was fixed shall not be credited to the employee when he re-enters service, and no such sum or any part thereof shall be used to provide a widow's annuity for any wife of the employee who has married the employee after such re-entry.
40 ILCS 5/12-146