A Certificate of Error corrects a mistake in what the county recorded about your property, or an exemption you were entitled to and did not receive. It is the route that stays open after the appeal window has closed, which makes it the answer to most "I missed the deadline" questions.
What it can correct
- A factual error on the county's record: wrong square footage, the wrong number of units, a building that has been demolished, or a property in the wrong class.
- A missing exemption — the Homeowner, Senior, Senior Freeze, Persons with Disabilities, Veterans and Home Improvement exemptions all qualify.
What it cannot do
It is not a second appeal. A Certificate of Error corrects something that is demonstrably wrong; it does not re-argue what your home is worth. If your case is that the assessment is too high compared with similar homes, that is an appeal, and the deadlines page shows when your township's window opens.
How far back, and what you get
The reach depends on the type. For a missing exemption the Assessor currently accepts tax years 2021 through 2025. For a valuation or characteristic error it is tax years 2022 through 2025 — the current year and three prior. Where the correction applies to a bill already paid, the Treasurer mails a refund check rather than reducing the next bill.
How to apply
Through the Cook County Assessor, with documents that prove the point — a survey, photographs, a closing statement, a birth certificate for an age-based exemption. Our full guide walks through the evidence each type needs: Certificate of Error: how to get a refund for a missing exemption. If you would rather we handled it, start with a free review; the fee is contingent on the refund.