If you own property in the South or West suburbs of Cook County, this is your reassessment year. There is no single countywide deadline to circle. There is a notice with your township's name on it, a last-file date printed on that notice, and roughly thirty days to act once it lands. The clock is already moving, township by township.
Quick Answer
In 2026 the South and West suburban townships are reassessed, and each opens its own appeal window when its notice mails (late April into summer, Riverside and River Forest first). You get about 30 days from the notice, with no extension. The fastest way to know where you stand is to look up your PIN.
Your notice is a value estimate, not a tax bill
The reassessment notice in your mailbox is the Assessor's estimate of your property's value. It is not your bill. Your eventual bill runs through several steps: value, multiplied by the assessment level for your property class, multiplied by the state equalization factor, multiplied by your local tax rate, minus exemptions.
For a sense of scale, Cook applies a 10% assessment level to residential property (Class 2) and 25% to commercial and industrial (Class 5) — Cook is the only Illinois county that splits levels this way, and the Illinois Constitution caps the top class at 2.5x the lowest. On top of that sits the state equalization factor, or "multiplier": the 2024 final Cook figure was 3.0355 (Illinois Department of Revenue). A change in your assessed value is the one lever an appeal addresses, and it flows through every step downstream. That is why the value on the notice is worth reviewing before the window closes — not the bill that arrives much later.
Why there is no countywide date
Cook reassesses on a three-year rotating cycle. The county is split into three groups — the City of Chicago, the North and Northwest suburbs, and the South and West suburbs — and one group is up each year. For 2026 it is the South and West suburbs. Cook is divided into 38 townships in all, and the offices process them one at a time rather than reassessing the whole group at once.
That staggering is why "the Cook County deadline" is the wrong thing to search for. Notices mail township by township from late April into summer, Riverside and River Forest first. Each township gets its own window of roughly 30 days from its notice, the last-file date is printed on the notice itself, and there is no extension. Miss it at the Assessor and that office's window is simply closed.
There is a second office, on a separate clock
After the Assessor's window for your township closes, the Cook County Board of Review opens its own, separate window for that township. A closed Assessor window does not mean the Board window is closed too. So at any moment your township might be open at one office, closed at the other, or not yet open at either — which is exactly why a single date written on the fridge tends to be the wrong one.
Who actually uses these windows
The public record makes the pattern plain. Censum's aggregation of the Board of Review appeal record covers 6,735,334 decisions across tax years 2010 through 2025. Countywide, about 86% of those appeals were filed with counsel. For the 17 South and West townships in the 2026 reassessment group specifically, the record holds 1,370,944 appeals, 73.0% of them attorney-represented.
And participation is lopsided. Of more than 1.8 million parcels, only roughly 18% to 32% are appealed in a typical year. The Treasurer's 2025 study found businesses appealed at 64% versus 27% for homeowners — a gap that quietly shifted about $1.9 billion of the burden onto parcels that did not appeal. None of that guarantees an outcome for any one property. It is base-rate signal: the owners carrying real tax tend to be the ones reviewing the value every cycle, and the window is the same one whether you review it or not.
What to do with your reassessment year
- Find your property by township, not just your city — windows open by township, and city lines do not match township lines.
- Read the last-file date off your notice and treat it as firm. There is no extension, and the Assessor and Board run separate windows.
- Look at the value, not the future bill. The assessed value is the one number an appeal touches.
- Decide before your window opens, so the decision is yours to make rather than one the calendar makes for you.
FAQ
Does my township reassess in 2026?
The 2026 reassessment group is the South and West suburbs of Cook County. If your property is in that group, your township is being reassessed this year and a notice will mail with your township's name and a last-file date on it. The fastest way to confirm your status is to look up your PIN or address.
When exactly does my appeal window open and close?
There is no single countywide date. Each township opens its own window when its notice mails — late April into summer, Riverside and River Forest first — and you generally have about 30 days from the notice. The last-file date is printed on the notice itself, and there is no extension. Confirm your specific dates on the official Assessor calendar.
Is the reassessment notice the same as my tax bill?
No. The notice is the Assessor's estimate of your property's value, not a bill. The bill is value multiplied by the assessment level, the state equalization factor, and your local tax rate, minus exemptions. An appeal addresses the assessed value, which is why the value is worth reviewing before the window closes.
If I miss the Assessor's window, is it over?
Not necessarily. After the Assessor's window for your township closes, the Cook County Board of Review opens its own separate window for that township. A closed Assessor window does not mean the Board window is closed. The two offices run on different clocks, which is why watching your specific township matters.
What does Censum do here, and what does it cost?
Censum is an independent property-tax intelligence and filing-rails vendor and Merchant of Record — not Cook County, not a government agency, and not a law firm. You can look up your PIN or address to see your township's reassessment status and where your appeal window stands. Pricing is flat.
Next step
There is no countywide deadline to memorize. There is your township, two offices, and a moving schedule — and in 2026, if you are in the South or West suburbs, it is your turn.
Look up your PIN or address with Censum to see your township's reassessment status and where your appeal window stands. Pricing is flat. Censum is an independent property-tax intelligence and filing-rails vendor and Merchant of Record — not Cook County, not a government agency, and not a law firm.