If a reassessment notice just landed in your mailbox, the most important thing to understand is what it is not. It is not a tax bill. It is the Assessor's new estimate of your property's value, and it starts a short clock you do not want to miss.
Quick Answer
A Cook County reassessment notice is a value estimate, not a bill. You have roughly 30 days from the notice date to file an appeal with the Assessor, and the last-file date is printed on it with no extension. Look up your PIN to confirm your township window before it closes.
In 2026, the South and West suburban townships are being reassessed. Notices mail township by township from late April through summer, starting with Riverside and River Forest. Each of the 38 townships runs on its own staggered window, so your neighbor in a different township may have a completely different deadline than you.
A notice is a value, not a bill
Your tax bill is built from several moving parts, only one of which is on this notice:
**Assessed value × state equalizer × local tax rate − exemptions = your bill.**
The notice gives you the value piece. For a home (Class 2 residential), Cook assesses at 10% of market value; commercial and industrial property (Class 5) is assessed at 25%. Cook is the only Illinois county that splits its levels this way, and the gap sits at the constitutional ceiling — the top class is capped at 2.5x the lowest. On top of that, the state applies an equalization factor (the "multiplier") — 3.0355 in the 2024 final figures from the Illinois Department of Revenue.
The practical point: a value that looks "a little high" gets multiplied through the rest of the formula before it ever becomes a bill. That is why the value on the notice is worth a careful read, especially if you carry real tax — a commercial parcel, a multi-unit building, or a portfolio where the numbers compound.
The clock is real and it does not stretch
The Assessor's appeal window is roughly 30 days from your notice. The exact last-file date is printed on your notice, and there is no extension. The Board of Review runs its own separate appeal windows later in the year, so missing the Assessor stage does not mean you have lost the whole year — but the two are different filings with different deadlines.
Because the windows are staggered by township, the only reliable way to know your deadline is to check your own parcel. A general "Cook County deadline" does not exist; there are 38 of them.
What actually supports a value challenge
An appeal is not "my taxes are too high." It is an argument that the Assessor's *value* is not well supported, paired with evidence. The strongest cases tend to lean on one of a few grounds:
- **Recent purchase.** If you bought recently at arm's length, the closing statement and sale price are direct evidence of market value.
- **Condition.** Photos of deferred maintenance, structural issues, water damage, or an outdated interior, plus repair estimates or inspection notes, can support a lower value.
- **Comparable sales.** Recent sales of genuinely similar nearby properties — same class, similar size, condition, and location — that sold for less than your implied value.
- **Uniformity (unequal assessment).** Similar properties assessed at lower values than yours. This is a math-and-comparables argument, and it is one of the more commonly filed grounds in Cook.
Not every case needs every item. A condition case may be photos and an estimate. A purchase case may be a single closing document. A uniformity case is about the comparables and the math.
A simple pre-filing packet
Before you decide anything, pull a clean picture of your parcel:
- The new assessed value from your notice and your prior value.
- Your property record (square footage, class, characteristics) — and whether any of it is wrong.
- Your sale documents, if you bought in the last few years.
- Photos of any condition problems and rough repair costs.
- A short list of comparable parcels and why each one is genuinely comparable.
If the Assessor's characteristics are wrong (over-stated square footage, a finished basement you do not have, a class that does not fit), that alone can be a clean correction.
How participation actually runs in Cook
You are not unusual for wanting to look. In a typical year only about 18-32% of Cook's 1.8M-plus parcels are appealed at all, and over 80% of the parcels that do appeal use professional representation. Across the 17 South and West townships up for reassessment in 2026, the public record shows 1,370,944 appeals, 73.0% of them attorney-represented.
The Treasurer's 2025 study found businesses appealed at 64% versus 27% for homeowners — and that gap shifted roughly $1.9B of the tax burden onto the people who did not appeal. None of that is a promise about your outcome. It is a signal: the owners who carry the most tax tend to be the ones who look, and the value on your notice is worth reviewing before the window closes.
FAQ
Is my reassessment notice a tax bill?
No. It is the Assessor's estimate of your property's value. Your actual bill is the value run through the state equalizer and your local tax rate, minus exemptions. The notice is the value step only.
How long do I have to appeal in Cook County?
Roughly 30 days from your notice date to file with the Assessor. The exact last-file date is printed on the notice and there is no extension. The Board of Review holds separate windows later, with their own deadlines.
Why does my neighbor have a different deadline?
Cook reassesses on a triennial cycle and mails notices township by township. There are 38 townships, each with its own staggered window. A neighbor in a different township can have a different last-file date.
Which townships are being reassessed in 2026?
The South and West suburban townships. Notices mail from late April through summer, beginning with Riverside and River Forest, then rolling through the rest on staggered schedules.
Do I need a lawyer to appeal?
That is your decision, and nothing here is legal or tax advice. The public record shows most appealing parcels use professional representation, but owners can file themselves. The first step either way is knowing your value, your deadline, and whether the case is worth making.
What evidence helps most?
It depends on the ground. Recent purchases lean on closing documents; condition cases on photos and repair estimates; and uniformity or sales cases on comparable parcels and the math that ties them to your value.
Check your parcel
Look up your PIN to see your parcel, your township's appeal window, and the signals worth reviewing before you decide. Censum is an independent intelligence and filing-rails vendor and Merchant of Record — not the County, not government-affiliated, and not a law firm. Pricing is flat.