Most owners argue an assessment one way: "this number is too high, my property would never sell for that." That is a real argument. But it is only one of two the Board of Review actually recognizes — and owners who only know the first one walk past the second, which is sometimes the stronger case.
The villain here is quiet. An over-assessment doesn't send a letter. It just sits inside the bill, compounding every year, until someone challenges it on the right ground. Picking the right ground is half the fight.
Quick Answer
The Board of Review recognizes two grounds. Overvaluation means the assessor's market value is higher than what the property would actually sell for. Lack of uniformity means your property is assessed at a higher level than comparable properties, even if the value itself looks right.
They are different arguments, they need different evidence, and they can both apply to the same parcel. Knowing which one — or both — fits your property is what separates a complaint that lands from one that doesn't.
Ground One: Overvaluation — The Value Itself Is Too High
This is the argument most people mean when they say their taxes are too high. In the State's own assessor-training material, the Illinois Department of Revenue (IDOR) calls it a **Fair Market Value complaint** — made "when the taxpayer believes the Estimated Fair Market Value of his or her property is greater than the property would sell for on the open market" (IDOR, *Board of Review Basic Course*, PTAX-1-BR).
You are not arguing about your neighbors here. You are arguing about your own property in isolation: the county says it's worth X, and you're showing it's worth less than X.
**What this ground needs as evidence.** The State lists the proof the Board will look at for a value case:
- A closing statement or settlement sheet from a recent purchase
- A recent appraisal report
- A list of sales of comparable properties
- Photos of elements detracting from value, with dollar estimates of their negative impact
A recent arm's-length sale, an appraisal coming in under the county's figure, or a tight set of comparable sales — that is the spine of an overvaluation case. The Board can also run its own market analysis and set the value itself.
Ground Two: Lack of Uniformity — You're Assessed Higher Than Comparable Properties
This is the ground owners miss, and it's a different animal entirely. IDOR calls it an **Assessment Equity complaint**, made "when the taxpayer believes his or her property is assessed at a higher rate than comparable property." And here is the line that matters most, quoted straight from the State's manual:
"This argument can be made even if the Estimated Market Value is accurate." (IDOR, PTAX-1-BR)
Read that twice. Even if the county's value on your property is dead-on what it would sell for, you can still have a winning appeal — if comparable properties around you are being assessed at a *lower level* than yours. Uniformity is the constitutional floor of the whole system: the board's duty, in the State's words, is "to review the degree of uniformity between individual assessments" so the tax burden is "equitably and uniformly distributed among all taxpayers within a taxing district." When your level is out of step with your peers, the burden isn't being distributed equitably — and that is its own valid complaint.
**What this ground needs as evidence.** Not sales — *assessment* comparables. The State spells out the Equity Analysis: pull the assessed value and above-ground square footage for roughly 25 comparable neighborhood properties (these are "not sales!" — they're property record cards), compute each one's **assessed value per square foot of building**, rank them, take the median, and see where your property lands. In the manual's worked example, the comparable median is **$40.29 per square foot**; a subject assessed at **$45.00 per square foot** sits visibly above the pack. That gap — not the headline value — is the case.
The State measures this same idea at the system level with the **Coefficient of Dispersion (COD)** — described by IDOR as "a statistical measure of variation of individual assessment ratios around the median level of assessments" and "the most common method used in measuring assessment uniformity." A high COD means properties are scattered widely around the median and are not uniformly assessed; a low COD means tight, fair, even assessment. You don't compute a COD to file — but it's the doctrine behind why being assessed above your comparable median is a legitimate grievance, not just sour grapes.
The Two Can Both Apply — and Should Be Checked Together
These are not either/or. A single parcel can be *both* valued too high *and* assessed at a higher level than its neighbors. Checking only the value question — "would it sell for that?" — leaves the uniformity question untested, and vice versa. The disciplined move is to run a property through both:
- **Overvaluation test:** Would this property actually sell, today, in its real condition, for the county's market value? If no — a sale, appraisal, or comp set is your evidence.
- **Uniformity test:** Is this property assessed at a higher level (per square foot of building) than comparable properties nearby? If yes — an assessment-ratio comparison is your evidence, *even if the value looks fair*.
A parcel that fails either test has a case. A parcel that fails both has two.
The Burden Is on You — Which Is Why the Right Ground Matters
The State frames property-tax claims as the applicant's to prove — its assessor-training manual states plainly that **"the burden of proof is on the applicant"** (IDOR, PTAX-1-BR). As a matter of practice, the Board doesn't go hunting for reasons to lower your number. You bring the ground, and you bring the evidence for *that* ground. An overvaluation argument backed by uniformity evidence — or the reverse — doesn't land. Naming the right ground, then matching it to the right proof, is the entire discipline of a clean appeal.
This is also where doing it alone gets risky. Under Illinois unauthorized-practice-of-law rules, **property owned by an entity — an LLC, a corporation, a trust, a condo association — generally must be represented by a licensed attorney before the Board of Review**; a business entity cannot appear for itself. And even individual owners are well served working with an attorney or a firm: the grounds, the comparable selection, and the evidence standards are exactly the kind of thing that's easy to get subtly wrong on your own. Censum prepares the case and works alongside your attorney or firm — Censum is not a law firm and is not your counsel of record.
Cook County Specifics (Mark These)
The core framework above is statewide — it's the State's method, and it applies in every Illinois county. A few Cook-specific facts to hold separately. Cook's classification percentages and equalization multiplier are external Cook County / IDOR figures, not from the assessor-training manuals, and they change — confirm the current numbers against the Cook County Assessor's classification ordinance and IDOR's latest final-multiplier release before relying on them:
- **Class levels.** Cook assesses by property type rather than at a single uniform percentage — for example, residential and commercial/industrial classes carry different statutory assessment levels under the county's classification ordinance. (Outside Cook, the statewide statutory level is **33.33%**, which *is* in the IDOR manuals.) Confirm the exact current class percentages for your property class with the Cook County Assessor before using them.
- **The multiplier.** Cook receives an annual state equalization multiplier from IDOR; the figure changes year to year, so check IDOR's most recent final-multiplier release for the year you're contesting. Note: the Cook County Assessor and Board of Review do not apply equalization themselves — the State's manual is explicit that "Cook County Assessor or Board of Review cannot equalize" (IDOR, PTAX-1-BR). Equalization is an IDOR function.
- **The window.** An assessment complaint is filed with the Board of Review within **30 days** after the assessment list is published, and you're contesting the **assessed value for the current year** — not the bill in your hand, which reflects a prior year. Cook's townships open and close on staggered schedules.
What to Do With This
Don't argue "my taxes are too high." That isn't a ground. Decide which of the two real grounds your property fits — value too high, level out of step with comparables, or both — and gather the evidence that ground actually requires.
The fastest way to see which way your case leans is to start with what the county has on record. Look up your property and Censum shows you the county's assessment, the valuation signal, and how your property compares — so you can tell whether you're looking at an overvaluation case, a uniformity case, or both, before you spend a dollar pursuing it. Censum prices appeals **flat** — never a percentage of any result — and nothing here is a guarantee of a reduction; the signal is research to help you decide, not a promised outcome.
FAQ
What's the actual difference between overvaluation and lack of uniformity?
Overvaluation is about your property in isolation: the county's market value is higher than what it would sell for, and you prove it with a sale, an appraisal, or comparable sales. Lack of uniformity is about your property relative to its neighbors: you're assessed at a higher level (per square foot of building) than comparable properties, and you prove it by comparing assessment ratios. The State recognizes both as valid grounds.
Can I win a uniformity appeal if the county's value is actually correct?
Per the State's own assessor-training manual, yes — an assessment equity argument "can be made even if the Estimated Market Value is accurate." If comparable properties are assessed at a lower level than yours, the unequal treatment is its own ground, independent of whether the headline value is right.
What evidence does each ground need?
Overvaluation: a recent purchase closing statement, a recent appraisal, a list of comparable *sales*, or photos of value-detracting conditions with dollar impact. Lack of uniformity: *assessment* comparables — the assessed value per square foot of building for roughly 25 comparable neighborhood properties, ranked against your own. Sales prove value; assessment ratios prove uniformity.
Who carries the burden of proof?
You do. The State's assessor-training manual states plainly that "the burden of proof is on the applicant." As a matter of practice, the Board doesn't build your case for you — you bring the ground and the matching evidence. That's why naming the right ground first, then matching the right proof to it, is the whole discipline.
My property is owned by an LLC (or trust or condo association). Can I file myself?
Generally no. Under Illinois unauthorized-practice-of-law rules, entity-owned property usually must be represented by a licensed attorney before the Board of Review — a business entity cannot appear for itself. Even individual owners are often better off working with an attorney or a firm, given the evidence standards. Censum prepares the case and works alongside your counsel; Censum is not a law firm and not your counsel of record.
Do you guarantee a reduction?
No. The assessment, valuation signal, and comparison data are there to help you decide which ground — if any — fits your property and whether it's worth pursuing. They are research, not a promise of any result. Anyone guaranteeing a property-tax outcome is overstating it.
Next Step
The owners who win aren't the ones who complain loudest about their bill. They're the ones who figure out *which of the two grounds* they actually have, gather the evidence that ground requires, and bring it inside the window — with counsel where it counts.
Check where your assessment stands to see the county's record, your valuation signal, and how your property compares. Censum is independent and is not affiliated with Cook County; nothing here is legal or tax advice.