Use this worksheet as a guide to figure your total withholding allowances you may enter on your Form IL-W-4. They didn't have access to their mail until we helped them fill out a withholding letter and they literally responded immediately to them.Tax Application and Affidavit Forms. Once completed, please submit the applicable form(s) below via email or mail to the address provided on the form. 4 ithholding Allowance. Use the following pages to complete your Illinois State and Federal income tax withholding, or W-4 information. Complete this worksheet to figure your total withholding allowances. Everyone must complete Step 1. All Illinois Courts must accept these forms. Chicago: University of Chicago Press.