You will need to file a nonresident Illinois state income tax return to get a refund of all the IL state income taxes withheld for the tax year in question. Employers are expected to withhold state income tax from an employee's wages if that employee is subject to state income tax unless noted below.Recent laws may not yet be included in the ILCS database, but they are found on this site as Public Acts soon after they become law. If any employee fails or refuses to furnish such information, the employer shall withhold the full rate of tax from the employee's total compensation. In your situation, if the employee provides Form ILW5NR, you can use the state listed on the form for the employee's state income tax. Find links to employee tax withholding allowance certificates (W-4 forms) for states other than Iowa and Illinois. Complete the worksheet on the back of this page to figure the correct number of allowances you are entitled to claim. Give your completed Form IL-W-4 to your. Having to comply with unique state taxes and wage laws can make processing payroll doubly daunting. Find links to employee tax withholding allowance certificates (W-4 forms) for states other than Iowa and Illinois.