Limits the amount of interest a lender can charge to the borrower. In Illinois the rate is 9%. However, there are so many exceptions to usury, that the only conceivable scenario is borrowing money to purchase groceries. In Illinois, if a usurious loan is extended to a borrower, the borrower may seek damages in the amount equal to twice the interest paid on the loan.
Exceptions to usury are R/E loans, business loans, loans to corporations, and many others. Read the statute to be sure.