Home Improvement Contractor - Licensed Contractors - Were do I find out if my contractor has a roofing license. I have looked up roofing licens and to many sites?

Were do I find out if my contractor has a roofing license. I have looked up roofing licens and to many sites?

I have looked up Il. roofing licens and I can not find anything that will say anything obout how you can see if your contracter has a licens