50 ILCS 45/60: Failure to file penalty.

If no return is filed before the issuance of a notice of tax deficiency or of tax liability to the taxpayer, any failure to file penalty may not exceed 25% of the total tax due for the applicable reporting period for which the return was required to have been filed. A local tax administrator may determine that the failure to file a return was due to reasonable cause and abate the penalty.