A: If you haven’t received an exemption on your property tax bill and you believe you are entitled to that exemption, you will need to submit a Certificate of Error with the Cook County Assessor’s Office (or the assessor’s office of the County where you live). You can file a Certificate of Error for the last four tax years online or via regular mail. You will need to submit a copy of your Driver’s License and other documentation (as required by the specific exemptions). It will take about six to eight weeks to receive your refund in the mail.