It's fast, easy, and free. You must file Form IL-1040-X, along with proper supporting documentation, for both corrected and amended returns.Tax collectors and taxpayers must file their tax returns electronically. To file an amended return for a previous year, please call our Business Contact Center. Filing: If you are efiling any of these forms, you will need to "flatten" the form so it cannot be changed after you complete it. Estate Tax Refund Requests: Requests for an Estate Tax refund must be made on a Petition for Estate Tax Refund Form (PDF fill-in form). Forms on this website are PDFs with fillable fields. Forms should be downloaded to your computer before filling in the fields. You may complete this form at home and mail or bring it to a Department of Human Services (DHS) office. (Attach separate sheets if necessary).