Please wait as long as you can to change your child to front-facing. The longer you wait, the more time you give your child's head, neck and spinal cord to fully develop...and the safer your child will be.
However, in the state of Illinois, there are no set weight or age requirements for rear-facing or front-facing. The law simply states that a child must be properly restrained.
Here's the actual wording from the State of Illinois:
Infants and Toddlers
Illinois law requires all children to be properly restrained in a child safety seat or booster seat until age eight. After age eight, Illinois law requires everyone under the age of 19 to be properly restrained anywhere in the vehicle. Currently, Illinois law does not require children to ride rear-facing to a set weight or age like some states. Illinois law does require that all children be properly restrained in child safety seats. The American Academy of Pediatrics and NHTSA strongly recommend that children stay rear-facing until they are BOTH over one year of age AND over 20 pounds to protect their fragile head, neck, and spinal cord.
More information on infant child safety seat safety
More information on forward-facing child safety seat safety
Illinois Child Passenger Protection Act
For more information regarding the state of Illinois car seat laws and guidelines, visit:
http://www.buckleupillinois.org/illaw.html