40 ILCS 5/3-110.11a
A police officer may establish optional credit for up to 5 years of service as a participant under Article 5, provided that the police officer (i) was certified under the law governing the certification of police officers at the time the service was rendered, (ii) applies in writing on or before December 31, 2023, (iii) supplies satisfactory evidence of the employment, (iv) completes 10 years of contributing service as a police officer as defined in Section 3-106, and (v) pays into the fund the amount the police officer would have contributed if he or she had been a regular contributor during such period, plus an amount determined by the Board to be equal to the municipality's normal cost of the benefit, plus interest at the actuarially assumed rate calculated from the date the employee last became a police officer under this Article.
A police officer may not establish credit under this Section for any service for which the police officer is eligible to receive benefits under Article 5 of this Code.
40 ILCS 5/3-110.11a