There is no single countywide deadline. Cook County sets appeal windows township by township, and each one is open for only a few weeks. Your deadline depends on which of the county's 38 townships your property is in — not your city or ZIP code.
Two windows a year, in order
- The Assessor opens a township's window when its assessment notices are mailed, and it stays open for several weeks (42 to 47 days in 2026).
- The Board of Review opens each township later in the year, after the Assessor has finished with it. You can file at the Board whether or not you appealed to the Assessor.
Late filings are not accepted at either stage: once a township's window closes, that stage is over for the tax year.
Find your date
Your date is printed on your assessment notice. For every township's current window — open, upcoming or closed — see our Cook County appeal deadlines page, updated as the county publishes. For how the 2026 cycle works, including which townships were reassessed, read the full 2026 guide.
If you have missed it
A missed window is not always the end. If the county's record of your property is wrong, or you were entitled to an exemption you did not receive, a Certificate of Error can still correct it after the appeal deadlines have passed.