50 ILCS 742/40

(a) Seniority points shall be based only upon service with the affected department and shall be calculated as of the date of the written examination. The weight of this component and its computation shall be determined by the appointing authority or through a collective bargaining agreement. (b) A seniority list shall be posted before the written examination is given and before the preliminary promotion list is compiled. The seniority list shall include the seniority date, any breaks in service, the total number of eligible years, and the number of seniority points.