Illinois has about 740 municipal police departments serving cities and towns of every size. In addition, there are over 100 other police agencies in the state. These serve many colleges and universities, railroad systems, parks, airports, zoos, transit systems, and water districts. Not every city has a police department; some contract with a neighboring city or their county sheriff’s department to provide law enforcement services within the incorporated area. In smaller cities, it is much more common to use the sheriff’s department, either with or without contracted services. Some of the police departments operate their own jail or detention facilities, especially in metropolitan areas, while others use the county jail. Although city police generally have jurisdiction only within the city limits and county sheriff’s department officers tend to limit their operations to unincorporated areas, many departments have a policy of mutual aid where they may operate within the other’s jurisdiction in times of need.
With over 41,000 sworn officers, Illinois provided 321 police officers per 100,000 residents, as of 2008. This was somewhat greater than the national average of 300 sworn officers per 100,000 residents. At that time, Illinois ranked fourth in the nation in the number of full-time sworn officers per capita. In crime statistics, Illinois, which is fifth in the nation in population, ranks 20th in violent crimes, 36th in burglaries, 33rd in larcenies, and 31st in auto thefts. Its highest ranking is 5th in the number of robberies. In overall crime index, the state ranks 24th.
Not surprisingly, the largest police department in Illinois is the Chicago Police Department, the second largest of its kind in the United States, ranking behind only the New York City Police Department. Chicago has over 12,000 sworn officers and about 2,000 other employees. It is also one of the oldest modern police forces in the world, with a history dating back to 1835. The department is led by the Superintendent of Police (appointed by the mayor), with the help of the first deputy superintendent. They oversee four bureaus: patrol, detectives, organized crime, and support services, each of which is led by a bureau chief. The Bureau of Patrol serves twenty-two districts. It also includes a special functions group; marine, helicopter, mounted and canine units, SWAT, and a traffic section. Ranks in the department below Bureau Chief are Deputy Chief, Commander, Captain, Lieutenant, Sergeant, Field Training Officer, Police Officer/Assigned, and Police Officer. The group designated Police Officer/Assigned includes detectives below the rank of sergeant who are assigned to special units such as violent crimes, robbery, gang and narcotics, internal affairs, and major accident investigation.