65 ILCS 5/10-2.1-18
When the force of the fire department or of the police department is reduced, and positions displaced or abolished, seniority shall prevail and the officers and members so reduced in rank, or removed from the service of the fire department or of the police department shall be considered furloughed without pay from the positions from which they were reduced or removed.
Such reductions and removals shall be in strict compliance with seniority and in no event shall any officer or member be reduced more than one rank in a reduction of force. Officers and members with the least seniority in the position to be reduced shall be reduced to the next lower rated position. For purposes of determining which officers and members will be reduced in rank, seniority shall be determined by adding the time spent at the rank or position from which the officer or member is to be reduced and the time spent at any higher rank or position in the Department. For purposes of determining which officers or members in the lowest rank or position shall be removed from the Department in the event of a layoff, length of service in the Department shall be the basis for determining seniority, with the least senior such officer or member being the first so removed and laid off. Such officers or members laid off shall have their names placed on an appropriate reemployment list in the reverse order of dates of layoff.
If any positions which have been vacated because of reduction in forces or displacement and abolition of positions, are reinstated, such members and officers of the fire department or of the police department as are furloughed from the said positions shall be notified by the board by registered mail of such reinstatement of positions and shall have prior right to such positions if otherwise qualified, and in all cases seniority shall prevail. Written application for such reinstated position must be made by the furloughed person within 30 days after notification as above provided and such person may be required to submit to examination by physicians, advanced practice registered nurses, or physician assistants of both the board of fire and police commissioners and the appropriate pension board to determine his physical fitness.
65 ILCS 5/10-2.1-18