Today, April 15th, is the deadline to file and pay federal and state income taxes. For federal filers needing an extension, the proper forms must be submitted with a payment of any estimated taxes owed to avoid any penalties or interest.
For Illinoisans needing an extension, the Illinois Department of Revenue has form IL-505-I which is for automatic extension payment. The form provides taxpayers who are unable to file their returns by the due date a means of calculating and remitting an estimated tax liability.