65 ILCS 5/11-1-7
The corporate authorities of any incorporated municipality, the boundaries of which are not co-extensive with any township, may contract with any such township in the county within which the municipality is located to furnish police protection outside of the incorporated municipality in such township.
The corporate authorities of any incorporated municipality situated in a county of fewer than 1,000,000 inhabitants may contract, with advice and consent of the sheriff in the county in which the request for contract services is made, based upon a determination of law enforcement needs of the area in which contract services are sought, with the county in which the municipality is located to furnish police protection in the county outside of the incorporated municipality.
65 ILCS 5/11-1-7