Blog · Research · 2026-09-02 · 7 min read

Do property tax appeals actually work? We counted 1,807,534 decisions

Appeal services advertise success rates above 80%. The Cook County Assessor publishes every decision it makes. We counted them: 23%.

Every company that files property tax appeals for a living advertises a success rate. They are uniformly excellent — 80%, 87%, "9 out of 10 clients see a reduction" — and they share one property: there is no way for you to check any of them. The number describes the cases that firm chose to take, counted by that firm, with no definition of success you are shown.

The Cook County Assessor publishes something better. Every appeal filed with the office becomes a public record: the case number, the township, the property class, the assessed value before and after, whether an attorney or agent filed it, the reason the office gave for its decision, and whether anything changed.

We downloaded all of them — 1,807,534 decisions covering tax years 2021 through 2026 — and counted. This article is what the count says. Everything in it can be reproduced from the Assessor's open data portal, and we have tried to be as clear about what the data cannot tell you as about what it can.

The headline number

Of 1,788,655 appeals the office decided, 411,358 produced a reduction in assessed value. That is 23.0%. Roughly one appeal in four succeeds.

It is worth sitting with the gap between that and the advertised figures for a moment. If a firm's real success rate were 87%, and the county-wide rate across nearly two million decisions is 23%, that firm would have to be almost four times better than the average of everyone filing — including every other professional firm, all of whom also advertise numbers in the eighties.

The likelier explanation is that "success rate" is being defined generously somewhere: cases screened out before filing are not counted, or a case moved to a later stage is counted as won, or the rate describes something other than the share of filings that produced a reduction.

Appeals have become much harder to win

The single most useful thing in this dataset is not the average. It is the trend, which is steep.

From 31.9% in 2021 to 16.2% in 2025 — the success rate roughly halved in four years, while the number of appeals filed stayed high. An owner relying on a friend's experience from 2021 is working from a market that no longer exists.

We cannot tell you from this data alone why it fell. Plausible contributors: assessments moved closer to market as the post-2020 price surge was absorbed into the rolls, so there was less error to find; appeal volume rose and offices tightened; and 2021 values were set during a period of unusual uncertainty that later corrected. The data shows the fall clearly and says nothing about the cause, and we would rather say that than offer you a tidy story we cannot support.

Where the property is matters enormously

Cook County is divided into 38 townships for assessment purposes. Success rates across them are not close.

An appeal in Jefferson Township succeeded four times as often as one in Palatine — 30.6% against 7.6% — in the same county, in the same year, under the same law and the same office.

This is the figure we would most want a homeowner to see before filing, and it is the one nobody publishes. It does not mean your Palatine appeal is hopeless; it means the base rate you are working against is very different from the county average, and you should calibrate your effort accordingly.

Why the spread exists is worth a little care. A township that was recently reassessed has fresher values and fewer errors to find. Townships differ in how uniform their housing stock is: a neighbourhood of near-identical post-war houses produces clean comparables and clean uniformity arguments, while a township of varied custom homes produces arguments the office can pick apart. And the mix of who files differs — a township with more commercial property has more professionally prepared appeals in the pool.

What a win is actually worth

The other number nobody publishes is the size of a successful reduction. Across 408,796 appeals that produced one:

The typical successful appeal reduces assessed value by 8.4%. A quarter of wins are under 5.7%, and a quarter are over 14.3%.

That is a smaller number than most people expect, and it is important for setting expectations honestly. On a Cook County home assessed at $30,000 — implying roughly $300,000 of market value under Cook's 10% residential level — an 8.4% reduction is about $2,520 of assessed value. Multiplied by the state equalisation factor and a mid-range composite tax rate, that is somewhere in the region of $570 a year.

Worth having, and worth roughly one evening of work. Not life-changing, and not the number an advertisement is likely to lead with.

Combining the two: is it worth filing?

The honest way to think about this is expected value: your chance of winning multiplied by what a win is worth, weighed against the effort.

In a township at the top of the table you are looking at roughly a 30% chance of an 8.4% reduction. In one at the bottom, under 8%. The saving is worth a few hundred dollars a year in most residential cases, and it recurs — a reduction generally holds until the next reassessment, so a single successful appeal in a three-year cycle is worth roughly three times its annual value.

That last point is the one most often left out, and it materially changes the arithmetic. A $570 annual saving that persists for a three-year cycle is about $1,700, for an evening's work and a filing that costs nothing at the Assessor level.

Against that: an appeal cannot raise your assessment at the Assessor stage, so the downside is your time. The realistic risk is not losing money but spending several hours on an argument that was never going to succeed — which is exactly what the base rates above are for.

How to check this yourself

Everything here comes from the Cook County Assessor's published appeal decisions, available on the county's open data portal as dataset y282-6ig3. It carries one row per appeal with the fields described at the top of this article. The parcel-level assessment history is in dataset uzyt-m557, which records mailed, certified and Board of Review values for every parcel and year, so you can see for yourself where a value changed and at which stage.

We publish the counts by township on our own precedent pages, updated when the county republishes. If our figures ever disagree with the county's, the county is right and we would like to know.

What we would tell a homeowner

Three things. First, ignore advertised success rates entirely, including any we might be tempted to publish about ourselves; the only rate that means anything is one you can verify against the county's own record. Second, look up your township before you decide how much effort to spend, because the base rate you are working against varies four-fold within one county. Third, expect a modest reduction rather than a dramatic one — the median win is 8.4%, and a service promising to halve your bill is describing something the county's own record says happens very rarely.

None of that is an argument against appealing. One in four succeeds, the process is free at the first stage, and the reduction persists. It is an argument for going in with an accurate picture of what you are doing, which is what this data gives you and what the advertising does not.