The 30-day rule: the deadline most owners miss
Your window opens when the township list is published, not when the notice reaches you.
More appeals are lost to the calendar than to the evidence. The deadline is short, it is not extendable, and missing it ends the matter outright for that year with no cure and no discretion.
The rule
In Illinois you generally have 30 days from the date your township's assessment roll is published to file with the Board of Review. Not 30 days from when your notice arrived, and not 30 days from when you opened it.
That distinction matters. Publication is a formal event: the county publishes the roll for a township, and the clock starts. Notices are posted around the same time, but postal delay is your problem, not the county's.
Why it is staggered
The roll is not published for a whole county at once. It publishes township by township, over months, in an order the county sets. So there is no single Illinois appeal deadline, and there is not even one deadline for your county — there is one for your township, and it will differ from your colleague's twenty minutes away.
This is the single most common way people miss it. They hear a date from a neighbour in another township and diary that.
Cook County has two windows
Cook runs two separate stages, each with its own period:
- The Assessor. Opens when your township's values are published and closes roughly 30 days later. Free, and an appeal here cannot raise your assessment.
- The Board of Review. A separate, later window with its own deadline. You may file here whether or not you appealed to the Assessor.
Missing the Assessor window does not end your year. This is worth knowing, because people who realise in July that they missed a May deadline often assume it is over. It is not.
Finding your date
- Your assessment notice states it. This is the authoritative source for your parcel.
- Your county assessor's or Board of Review's website publishes the township schedule, usually as a table of open and close dates.
- Call and ask. Offices answer this question constantly and will tell you.
What "filed" means
Filed by the deadline, not posted by it. Many counties now require or prefer online filing, which timestamps the submission and removes the argument entirely. Where paper is used, check whether the county treats a postmark as filing or requires receipt — the two are different and the difference has ended appeals.
If you have already missed it
Three things are still available, and people rarely know about the third.
The next stage. If you missed the Cook Assessor window, the Board of Review window is separate and later.
Next year. Assessments can be appealed annually, not only in reassessment years. If your value is carried forward and you believe it is wrong, next year's window is a real opportunity rather than a consolation.
A certificate of error. This is the one people miss. Where the assessment contains a factual error — a floor area that was never right, a building that no longer exists, an exemption that should have been applied — several counties allow correction outside the appeal window entirely, often for prior years as well. It is a different process with a different form, and it is not governed by the 30-day rule. If your complaint is "the record is wrong" rather than "the value is too high", ask about this before assuming you have run out of time.
The practical advice
When your notice arrives, do one thing before reading anything else: find the deadline and put it in your calendar with a reminder two weeks earlier. Everything else on the page can wait; that cannot.