A reassessment notice lands in the mailbox and most owners do one of two things: nothing, or panic. Both are expensive.
The notice is not a bill. It is a value estimate, and it opens a clock you do not control.
Quick Answer
A Cook County reassessment notice is a proposed value, not a tax bill. It opens two appeal windows: first the Assessor (about 30 days from the notice, last-file date printed on it, no extension), then the Board of Review later. Look up your PIN to see whether the new value is worth reviewing.
Your actual bill is not on that notice. It is the proposed value times the assessment level times the state equalizer times the local tax rate, minus exemptions. A higher value does not automatically mean a proportionally higher bill, and a value that looks "fine" can still be out of line with comparable parcels. The notice is the signal; the windows are where anything happens.
What the notice actually is
Cook reassesses on a triennial cycle, one third of the county each year. For 2026, that is the South and West suburban townships. Notices mail township by township, starting in late April and rolling through summer, with Riverside and River Forest going out first.
When yours arrives, it carries a proposed assessed value. To get from that to a tax bill, the county applies the assessment level (10% for most homes, 25% for commercial and industrial property), then the state equalization factor (the "multiplier" was 3.0355 final for 2024), then your local tax rate, and finally subtracts any exemptions you qualify for. So the number on the notice is one input, not the outcome.
That distance between "value estimate" and "what I owe" is exactly why a notice should be read as information, not as a verdict.
The first window: the Assessor
The reassessment notice opens an appeal window at the Assessor's office. It is short. The window runs roughly 30 days from the date your notice mails, and the last-file date is printed on the notice itself.
There is no extension. Miss the printed date and that round is closed for the year. The windows are staggered by township, so your neighbor in the next town over may have a completely different deadline than you do. This staggering is the single most common reason owners miss the window: they assume a "Cook County deadline" exists when in fact there are 38 of them on different days.
The second window: the Board of Review
After the Assessor window closes, the Cook County Board of Review opens its own separate appeal windows, again township by township. This is a second, independent bite at the value, with its own filing rules and its own clock.
Censum's aggregation of the public Board of Review record shows how heavily this lane is used: 6,735,334 decisions across tax years 2010 through 2025. For the 17 South and West townships up for 2026 reassessment, that record holds 1,370,944 appeals. So this is not an obscure process; it is a well-worn one with a deep public history.
How owners actually behave at the Board
The same public record carries a signal worth knowing before you decide. Across the county, about 86% of appealed parcels are filed with professional representation rather than pro se; in the 2026 South and West townships specifically, 73.0% of appeals were attorney-represented.
There is a participation gap underneath that. Of more than 1.8 million Cook 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 difference the study tied to roughly $1.9 billion of tax burden shifting onto the parcels that did not appeal. None of that is a promise about any single property. It is base-rate context: a large share of value challenges in Cook come from owners who carry real tax and treat the windows as routine.
What to weigh before you decide
The notice gives you a value and a deadline. Whether to act on it is a judgment about your specific parcel, not a reflex. Useful questions:
- Does the proposed value line up with what comparable parcels in your township are carrying, or is it an outlier on the high side?
- How much tax actually rides on the difference once the level, equalizer, rate, and exemptions are applied?
- Did your exemptions carry through correctly, or did something drop off?
- Which window are you in right now, and what is the printed last-file date?
- Is the evidence on your side strong enough that a review is worth the effort, or is the value defensible?
If you carry meaningful tax, commercial property, a portfolio, or simply want to know where your parcel stands before the clock runs, the fastest first move is to look it up.
FAQ
Is my reassessment notice the same as my tax bill?
No. The notice is a proposed value. Your bill is that value times the assessment level (10% residential, 25% commercial and industrial) times the state equalizer (3.0355 final for 2024) times your local rate, minus exemptions. A higher proposed value does not translate one-for-one into a higher bill.
How long do I have to appeal in Cook County?
The Assessor window runs about 30 days from when your notice mails, and the exact last-file date is printed on the notice. There is no extension. Windows are staggered by township, so there is no single countywide deadline.
Which townships are reassessed in 2026?
The South and West suburban townships. Notices roll out township by township from late April through summer, with Riverside and River Forest first.
Do I get a second chance after the Assessor window closes?
Yes. The Cook County Board of Review opens its own separate appeal windows after the Assessor's, again by township, with its own rules and deadlines. It is an independent review of the value.
Should I appeal on my own or use a professional?
That is your call and depends on your parcel and your comfort with the process. As context, the public record shows about 86% of appealed parcels countywide are filed with professional representation, and 73.0% in the 2026 South and West townships. Censum is an independent intelligence and filing-rails vendor, not a law firm, and this is not legal or tax advice.
What does looking up my PIN actually tell me?
It surfaces the signal on your specific parcel: how the proposed value sits relative to comparable parcels, what the public appeal history around it looks like, and where you are in the window. It is a read of where you stand, so you can decide whether a review is worth it before the no-extension clock runs.