Illinois was never supposed to have an income tax, and didn't have one until 1970. Our property taxes are very high for that reason.
4.95% flat rate is pretty high.
the states around illinois have a higher income tax, but they also have a progressive tax system which lessens the pain for lower income households.
The state income tax is not used for education, which is individually funded by counties via property taxes, which more than make up the difference.
The income tax is low, but property and sales taxes are also high. Want to buy a drink in Chicago? You're going to pay around a 12% tax on that drink. In Illinois, they get you coming and going.