There are 2 types of red light violations: right turn on red without coming to a complete stop, and entering an intersection after the traffic signal has turned red.
You may be cited with a red light violation if you fail to bring your vehicle to a complete stop before turning right when the light is red. Turning right on red, after bringing your vehicle to a complete stop, is only allowed at intersections that do not have signs prohibiting such turns. For exact wording, please check Illinois' Rules of the Road, or visit the Secretary of State's website Cyber Drive Illinois.
Motorists already in the intersection when the signal changes to red, when waiting to turn for example, are not considered red light violators.
Cyber Drive Illinois