70 ILCS 705/16.16a
(c) A person who is on disability leave or military leave granted by the board and who wishes to return to active duty in his position, if otherwise qualified, shall be reinstated to his position at the rank or grade held at the start of the leave, not more than 60 days after his written request for reinstatement is filed with the board. Such request shall be filed not more than 30 days after termination of the disability or military or naval service. If the leave was for an injury or illness incurred in the performance of duty or because of military or naval service, the person shall be credited with seniority in the department and in his rank or grade for the period of such leave.
If a fire department is at full strength, the procedure would be to place the last person hired on furlough and reinstate the returning serviceman or woman.
(from Ch. 127 1/2, par. 37.16a)
(Source: P.A. 86-562.)