430 Illinois Compiled Statutes § 135: 
New and existing single- and multi-family dwellings with fuel-burning appliances are required to install at least one operable, approved CO alarm within 15 feet of every room used for sleeping purposes. The Illinois State Fire Marshal interprets this to include all buildings that contain sleeping units: single family homes, condominiums, multi-family dwellings, hotels, motels, nursing homes, prisons, etc. Dwellings without fuel-burning appliances or attached garages are not required to have CO detectors. (Effective date: January 1, 2007)