Illinois Contractor Licensing Requirements

[Sam Patel]

I'm near Chicago suburbs (DuPage county) and I'm looking to rehab a potential property. For what type of work when dealing with contractors in Illinois require licensing (e.g. electric, HVAC etc...)? Do you need a license for basic dry wall installation, flooring installation, install door and so on? I'm thinking no, but I wanted to confirm.

If a contractor says they are licensed, how do I check they are? Thanks for the feedback in advance.