By James W. Chipman

There’s a remedy for correcting errors or mistakes in a property tax assessment even after the deadline for appealing to the board of review has passed.

Mistakes happen. If a mistake occurs in the property tax process, it could be costly if not corrected. Fortunately, they are fixable, thanks to a what is known as a Certificate of Error, or in property tax parlance, a C of E. When an assessment error is discovered and brought to the attention of local assessing officials, taxpayers can obtain relief through a C of E.


A Certificate of Error is a written acknowledgement by either the county supervisor of assessments (chief county assessment officer) or the board of review that something is wrong with your assessment. The C of E law can be used to correct problems such as mathematical errors, incorrect descriptions of property, duplicate assessments, and improvements that have been damaged or destroyed. It also can apply to cases where an exemption for which a property was eligible, but the exemption was not applied to the tax bill.

There are some instances that cannot be remedied by a C of E, including “errors of judgment as to the valuation of the property.”* Ordinary valuation disputes about market value or lack of uniformity can only be resolved by filing an appeal with the board or review and the state Property Tax Appeal Board (PTAB).


In Illinois counties outside of Cook County, the C of E process is initiated whenever the supervisor of assessments or the board of review discovers an error, or upon the taxpayer’s initiative. A C of E requires the approval of the supervisor of assessments and a majority of the board of review. It is then forwarded to the county clerk and treasurer.

Interestingly, a taxpayer isn’t entitled to notice and an opportunity to be heard. In fact, local assessing officials can fix a mistake without the taxpayer’s knowledge or input. Should the county treasurer refund money because of a C of E, the taxpayer is entitled to 0.5% interest per month.**


Generally, a C of E can be issued “at any time before judgment or order of sale is entered” in a proceeding to collect unpaid taxes on a property.*** The term “judgment” refers to the annual tax sale that typically takes place within 60 days after the second installment of taxes is due.

While local assessing officials must act before the annual application for judgment, a 1977 Illinois Attorney General opinion added a further limitation finding that the period in which a C of E may be issued expires when a taxpayer files an appeal with the PTAB or when the PTAB renders a decision.****

Like it or not, the property tax process is prone to mistakes. That’s why an annual review of your property assessment and tax bill for accuracy is time well spent.

If you find an error or mistake on either of your documents, contact Donald T. Rubin at or 312.696.2641 for advice on whether a C of E is the best way to remedy your situation.

*35 ILCS 200/14-20 (The certificate of error process differs in Cook County – see 35 ILCS 200/14-10 & 200/14-15)
**35 ILCS 200/20-178
***35 ILCS 200/14-20
****IL Atty. Gen. Op. No. S-1307 (1977)