Your Illinois filing period is the same as
your federal filing period. Illinois will assume that you
are filing your Form IL-1040 for the calendar year unless
you indicate a different filing period in the space provided
at the top of the return. The due date for 2010 calendar
year filers is April 18, 2011.
You are granted an automatic six-month extension in which to file your Form IL-1040, Individual Income Tax Return. An extension of time to file is not an extension of time for payment of Illinois income tax. You must use Form IL-505-I, Automatic Extension Payment for Individuals, to pay any tax you owe in order to avoid penalty and interest on tax not paid by April 18, 2011. If you do not expect to owe tax, you do not have to do anything.