20 ILCS 2610/20
The Illinois State Police from time to time may enter into contracts with The Illinois State Toll Highway Authority, hereinafter called the Authority, with respect to the policing of toll highways by the Illinois State Police. Such contracts shall provide among other matters for the compensation or reimbursement of the Illinois State Police by the Authority for the costs incurred by this State with respect to such policing service, including, but not limited to, the costs of: (1) compensation and training of the State policemen and the clerical employees assigned to such policing service; and (2) uniforms, equipment, and supplies, which shall be Illinois State Police property, and housing used by such personnel; and (3) reimbursement of such sums as the State expends in connection with payments of claims for injuries or illnesses suffered by such personnel in the line of duty. Each such contract may provide for the methods of ascertaining such costs, and shall be of such duration and may contain such other appropriate terms as the Illinois State Police and the Authority may agree upon. The Illinois State Police is not obliged to furnish policing service on any highway under the jurisdiction of the Authority except as required by contract.
20 ILCS 2610/20