20 ILCS 2610/16
State policemen shall enforce the provisions of the Illinois Vehicle Code and Article 9 of the Illinois Highway Code and shall patrol the public highways and rural districts to make arrests for violations of the provisions of such Acts. They are conservators of the peace and as such have all powers possessed by policemen in cities, and sheriffs, except that they may exercise such powers anywhere in this State. The State policemen shall cooperate with the police of cities, villages, and incorporated towns, and with the police officers of any county, in enforcing the laws of the State and in making arrests and recovering property. They may be equipped with standardized and tested devices for weighing motor vehicles and may stop and weigh, acting reasonably, or cause to be weighed, any motor vehicle which appears to weigh in excess of the weight permitted by law. It shall also be the duty of the Illinois State Police to determine, whenever possible, the person or persons or the causes responsible for the breaking or destruction of any improved hard-surfaced roadway and to arrest all persons criminally responsible for such breaking or destruction and bring them before the proper officer for trial. The Illinois State Police shall divide the State into zones, troops, or regions and assign each zone, troop, or region to one or more policemen. No person employed under this Act, however, shall serve or execute civil process, except for process issued under the authority of the General Assembly, or a committee or commission thereof vested with subpoena powers when the county sheriff refuses or fails to serve such process, and except for process allowed by statute or issued under the authority of the Illinois Department of Revenue.
20 ILCS 2610/16