You decide: Quoted from the Illinois DNR 2003-2004 hunting digest:

It is unlawful to use lights of, any light from, or any light connected to a vehicle or conveyance in any area where wildlife can be found. This does not prohibit normal use of headlamps for driving upon a roadway. EXCEPT: Skunk, opossum, red or gray fox, coyote and raccoon may be taken during the open season by the use of a small hand-operated light by a person who is on foot and not in any vehicle.

My interpretation of this is that you can NEVER use a spotlight attached to a vehicle (or conveyance like mountain bike) but CAN use battery powered lights for other legal hunting of Coyote etc. Coyote is legal to hunt at night with a spotlight between Nov 10th and Jan 31st (same as Red and Gray Fox) but is closed during whitetail firearm season. However, if a conservation officer saw you spotlighting a deer at any time I would expect a prompt ticket!