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What is an Illinois W-4 Personal Withholding Allowance Form and how do I complete it?

There is also an Illinois W-4 form for state taxes: IL-W-4 Employee's Illinois Withholding Allowance Certificate. This state form can be found on our Web site: or directly at: The number of allowances claimed on both W-4 forms determines the amount of taxes that will be withheld.

The more allowances claimed, the less tax that is withheld. However, the IDRS has requirements that employees have to pay in a sufficient percentage of tax due for the year or face penalties.