IL is the written short form of Illinois, a state in the United States. Chicago sits in the north of it, beside Lake Michigan; the capital is Springfield. You will see IL on envelopes, forms, maps, sports pages, and news when space is tight: Chicago, IL. People almost never say the two letters out loud when they mean the state; they say Illinois. The two-letter form follows the US postal style (CA for California, NY for New York, and so on). Though actually, IL can mean other things in other lists — in some country codes it is Israel, and in grammar il- is a prefix in words like illegal — but this entry is only the American state.