Section 35 ILCS 735/3-10 - Limitations(a) In the case of a false or fraudulent return with the intent to evade tax, the tax may be assessed at any time.(b) In the case of a failure to file a return required by law, the tax may be assessed at any time. If the taxpayer shows that there was reasonable cause for failure to file a return, the period shall be limited to not more than 6 years after the original due date of each return required to have been filed.(c) In the case of a failure to file a return required by law that is voluntarily disclosed to the Department, in accordance with regulations promulgated by the Department for receiving the voluntary disclosure, the tax may be assessed no more than 4 years after the original due date of each return required to have been filed.(d) The limitations on assessment shall not apply where the Department has, within the 6-year period of limitation, notified a person that a return is required by law from that person. These limitations shall be tolled for any time period in which the order of any court has the effect of enjoining or restraining the Department from that assessment.