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You will need to register with the Illinois Dept. of Revenue. Here is the way to contact them.
Since you will be selling retail you will need to collect sales tax and file sales tax returns.
You did not say how you were going to structure your business. You could be a sole proprietorship. The advantage is simplicity. The disadvantage is that all your personal assets are at risk if the business fails. I recommend that you either incorporate and operate as a Sub Chapter S corp. or form a limited liability company. Both of those entities provide you the benefit of limited liability so your personal assets are not at risk unless you decide to personally guarantee a company debt.
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