How property tax appeals
actually work in Cook County.
Every step, every timing window, every mistake we see homeowners make. Twelve minutes to read. Built from the Board of Review's procedural rules, Cook County's triennial reassessment schedule, and 107,430 BOR decisions from 2024.
- 01. Cook County reassesses each of 38 townships every three years — staggered, so one-third of the county reassesses each year.
- 02. You get a Reassessment Notice in the mail. That number drives three years of tax bills.
- 03. You have roughly 30 days to file an appeal with the Assessor, then a second 30-day window with the Board of Review.
- 04. Whether your appeal wins is almost entirely about evidence quality — comparable sales, ratio studies, uniformity arguments.
- 05. The BOR issues a written decision 60–180 days after filing. If reduced, the adjustment flows to the Clerk, who recomputes your bill. Refunds on already-paid taxes typically land within 60 days of decision.
The triennial reassessment
Cook County is divided into three reassessment groups: the city of Chicago (reassessed in one year), the north and northwest suburbs, and the south and west suburbs. Each group is reassessed every third year. In off-years, your assessed value is typically carried forward with minor adjustments.
The reassessment year matters. It's when new comparable sales are ingested, when the Assessor's AVM re-runs, and when most of the swings happen. A triennial year is also the best appeal year — the Assessor has just committed to a new number that must be defended, and the data used to build it is freshest.
Check your Censum score during your triennial year specifically. A high score in a non-reassessment year is still worth filing, but the signal is strongest when fresh comparables are being weighed.
The reassessment notice arrives
You'll get a mailed notice — officially the Notice of Proposed Assessed Valuation — from the Cook County Assessor's office, usually between February and September depending on your township. It lists the new assessed value, the property characteristics used to derive it, and your appeal deadline with the Assessor.
Read the property characteristics carefully. Square footage, number of bathrooms, land area, and building condition are entered manually and are often wrong. A mis-recorded feature is one of the cleanest appeals you can file: you provide documentation (MLS, a survey, photos) and the Assessor's office typically corrects it administratively.
Waiting for the actual tax bill to arrive before appealing. By the time you see the bill, both the Assessor's and Board of Review's appeal windows have usually closed for the year. The reassessment notice is the trigger, not the bill.
Two appeal windows: Assessor, then Board of Review
There are two separate appeal venues, each with its own window, rules, and success rate. You can file at one, the other, or both — they are independent proceedings.
Informal, administrative review. Grants are common for clear errors (incorrect characteristics, obvious comparable issues). Denial does not preclude a BOR filing — many strong cases are filed only at BOR.
Quasi-judicial. A three-commissioner panel reviews the evidence. Sworn hearings are rare for residential — most residential appeals are decided on the written packet alone. This is the primary venue for strong cases.
Censum's pre-filled form targets the Board of Review — the venue where evidence quality matters most and where our 86.1% top-decile precision comes from BOR decisions specifically. For properties with a straightforward Assessor's Office case (characteristic errors), we flag it in the packet so you can file both.
What actually wins an appeal
The Board of Review weighs three lines of evidence, in rough order of weight:
- Recent arms-length sales of comparable properties. The single strongest argument. If three or four genuinely comparable nearby properties sold recently for materially less than your assessment implies, that is very hard to argue against.
- Township-level ratio studies and equity. If the effective assessment level in your township is systematically higher than neighboring townships, that's a uniformity argument the BOR has a long history of granting.
- Assessment history and trend. A year-over-year jump well above the township average requires justification (permit, characteristic change) that the Assessor's office often can't produce. Unexplained spikes are appealable.
Weak appeals rest on anecdote ("my neighbor's house is bigger"), emotion ("my taxes are too high"), or unsupported comparables (different school district, different property class). The BOR has rules against those; they fail at scale.
Decision, bill recalculation, refund
The Board issues a written decision in roughly 60 to 180 days. If your assessed value is reduced, the Clerk of the County applies the new number to your tax extension. If the tax bill for that year has not yet been issued, the bill is generated at the lower number. If you have already paid, a refund is issued — typically in the 30–60 days following the Clerk's processing.
The reduction persists until the next triennial reassessment in your township — typically two more tax years at the reduced level. That is why the lifetime value of even a small reduction compounds so quickly.
A BOR denial can be escalated to the Property Tax Appeal Board (PTAB) — a state-level venue with longer timelines (12–24 months) and stricter evidentiary standards. PTAB is outside Censum's standard packet; it generally justifies an hourly attorney engagement rather than a flat fee. Our Tier A credit-forward guarantee applies instead: your $199 rolls to next year's filing.
Source: 222,000 Cook County SFH Board of Review decisions, 2024 filing year. Reduction granted = net assessed value reduction ≥ $100 after BOR review. The unconditional 48.4% grant rate is why generic "everyone should appeal" advice works — but Censum's model lifts top-decile precision to 86.1%, which is where flat-fee economics actually pay off.
- —Waiting for the tax bill. By then your appeal window has usually closed. File when the reassessment notice arrives.
- —Using emotional arguments. "My taxes are too high" is not a ground for reduction. Evidence is.
- —Picking the wrong comparables. Different school district, different property class, or stale sales all fail. Recent, same-class, same-submarket is the standard.
- —Signing a 30% contingency for a reduction that repeats. A Cook County BOR reduction typically survives the remainder of the triennial. You're paying a percentage every year for a fight you already won.
- —Skipping the Assessor filing when there's a clear error. Incorrect square footage or bathroom counts are fixed administratively at the Assessor's office. Those cases don't need the BOR.
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