520 ILCS 5/1.15
All authorized employees of the Department, duly accredited officers of the U. S. Fish and Wildlife Service, and all sheriffs, deputy sheriffs, and other peace officers shall be empowered to arrest any person detected in violation of any of the provisions of this Act, including administrative rules.
All such officers shall make prompt investigation of any violation of the provisions of this Act, including administrative rules, reported by any other person, and cause a complaint to be filed before the Circuit Court having jurisdiction thereof in case there seems just ground for such complaint and evidence procurable to support the same.
Upon the filing of such complaint, such officers shall render assistance in the prosecution of the party against whom complaint is made.
Peace officers, but no employee of the Department, making arrests and serving warrants provided for by this Act shall receive the fees and mileage as provided by law for sheriffs.
Each duly accredited officer and authorized employee of the Department is authorized to execute and serve all warrants and processes issued by any Circuit Court.
In the performance of their law enforcement duties under this Act, authorized employees of the Department may operate vehicles owned or leased by the Department upon a highway, other than an interstate highway, limited access highway, State highway or any highway within the limits of an incorporated area, during hours of darkness without lighted headlamps, tail lamps and clearance lamps, notwithstanding the provisions of Article 12 of The Illinois Vehicle Code if so operating such vehicles will aid in the accomplishment of a lawful arrest for violation of this Act or subsequent administrative rules or in ascertaining whether a violation of this Act or subsequent administrative rules has been or is about to be committed and when it will not endanger the public health, safety and welfare.
520 ILCS 5/1.15