If you own property in Cook County and your reassessment notice came in higher, "my assessment is too high" can mean two genuinely different things. They are argued differently, they use different evidence, and one can apply to your parcel even when the other does not. Knowing which one you have — before your township's window closes — is the difference between a focused review and a pile of paper.
This matters most in 2026 for South and West suburban owners. Cook reassesses on a three-year cycle, and 2026 is the South and West triennial. Notices mail township by township from late April into summer (Riverside and River Forest first), and each of the 38 townships has its own staggered window — roughly 30 days from the notice, with the last-file date printed right on the notice and no extension.
Quick Answer
In Cook County, "too high" can mean two things: over-valuation (the Assessor's value is above what your property would sell for) or lack of uniformity (it is assessed higher than comparable nearby parcels). Each uses different evidence. Look up your PIN to see which fits before your window closes.
A reassessment notice is a value estimate, not a tax bill. Your bill is value times the assessment level times the state equalizer minus exemptions, applied to a local rate — so a higher notice is a signal worth reviewing, not a settled number.
Over-valuation is the price story
An over-valuation argument says the Assessor's market value is simply too high for what your property is — given its size, condition, location, and what comparable properties actually sell for. This is the version most owners picture first.
Evidence that tends to support it:
- a recent purchase price (a closing near the assessment date is strong)
- nearby sales of genuinely similar properties
- condition problems — photos, repair estimates, inspection reports
- characteristics the Assessor has wrong (square footage, bedroom/bath count, building class, land area)
- a recent independent appraisal
The mechanics underneath: Cook applies a 10% assessment level to residential (Class 2) property and 25% to commercial and industrial (Class 5). Cook is the only Illinois county with split levels, and it sits at the constitutional cap — the top class can be no more than 2.5x the lowest. So the Assessor's stated market value is the lever; the level and the 2024 final state equalizer of 3.0355 are applied on top of it.
Lack of uniformity is the fairness story
Uniformity is the more technical argument, and it is distinctly an Illinois one. Here you are not only saying your property is worth less — you are saying it is assessed higher than comparable properties around it. Even if the market value is defensible, uniform treatment is its own basis for review.
This one lives or dies on comparable discipline. Same subdivision is not enough. Useful comparables are genuinely alike in size, age, construction quality, condition, and property type — and assessed lower per unit than yours. A handful of clean, well-matched comparables outweighs a long list of loose ones.
Both can be true — keep them separate
A single parcel can be over-valued and non-uniform at the same time, and it is fine to raise both. What is not fine is mixing them into one blurry complaint. Keep the lines clean:
- "Here is why the market value is too high." (over-valuation)
- "Here is why my assessment is out of line with comparable properties." (uniformity)
- "Here is the value the evidence supports."
A reviewer needs an organized argument, not a screenshot pile.
Why this is worth doing at all
Appeal participation in Cook is lopsided. Of 1.8 million-plus parcels, only about 18–32% are appealed in a typical year. The Treasurer's 2025 study found businesses appealed 64% of the time versus 27% for homeowners — a gap that shifted roughly $1.9 billion of burden onto owners who did not appeal. Across Censum's aggregation of the public Board of Review record (6,735,334 decisions, tax years 2010–2025), over 80% of appealing parcels used counsel; for the 17 South/West townships up in 2026, 73.0% of the 1,370,944 appeals were attorney-represented. None of that predicts your outcome. It does say the owners who carry real tax tend to be the ones who look — and the ones who do not look absorb what the lookers shed.
FAQ
Is my reassessment notice my new tax bill?
No. It is the Assessor's estimate of value. Your bill is value times the assessment level (10% residential, 25% commercial/industrial) times the state equalizer (3.0355 final for 2024) minus exemptions, applied to your local rate. A higher notice is a signal to review, not a final amount.
What is the difference between over-valuation and lack of uniformity?
Over-valuation says the Assessor's market value is too high for your property. Lack of uniformity says your property is assessed higher than comparable nearby properties, even if its value is defensible. They use different evidence, and either or both can apply to one parcel.
When does my Cook County appeal window open in 2026?
2026 is the South and West suburban triennial. Notices mail township by township from late April into summer, and each township has its own window — about 30 days from the notice. The last-file date is printed on the notice and there is no extension. The Board of Review runs separate windows afterward.
Do I need a lawyer to look at this?
Not to look. Looking up your PIN to see whether the over-valuation or uniformity signal fits is something any owner can do. Most appealing parcels countywide are represented by counsel, but that is a choice you make after you understand what your parcel shows — not a prerequisite to checking.
What's the fastest way to see which signal applies to me?
Look up your PIN. Censum reads the public assessment and Board of Review record for your specific parcel and surfaces whether an over-valuation or uniformity signal is present, so you are reviewing your own facts rather than a generic explainer. Censum is independent and is not affiliated with Cook County.