Illinois has a number of forms that are required for different purposes. Some of the most common are the Illinois income tax form, Form IL-1040, and the Illinois vehicle registration form, Form VSD 190. Knowing which forms to use and when to use them can be confusing, so it's important to familiarize yourself with the requirements before you submit any paperwork. The Illinois Department of Revenue (IDOR) website has all the information you need, including forms and instructions. You can also contact IDOR's Customer Service Center if you have any questions.