Property Tax Buddy

What actually happens to Cook County property tax appeals

Published August 3, 2026 · Property Tax Buddy · Built from the Cook County Assessor's own published records

Cook County publishes the result of every single appeal it decides, with the value before and the value after. Almost nobody reads it. So we went through all 351,196 residential ones from 2024, split the houses out from the condos, and worked out what really happens when a homeowner appeals.

The short version

Roughly one in five people who take an appeal all the way to a decision get something out of it. Which also means about four in five spend their time and get nothing, and you can find out which group you're in before you spend an afternoon on it.

Where these numbers come from

Now the Cook County Assessor publishes an appeals dataset with every case going back years, and it carries the value the county first mailed you right alongside the value it certified after your appeal. Which means you can just count how often those two numbers end up different, and that's basically what we did.

Also, we split the houses from the condos, because a lot of published figures don't. Cook County hears appeals on everything from a bungalow to an office tower, and if you mix all of that together you end up with a number that describes commercial landlords about as much as it describes you. So everything below is residential only, and we're counting houses and condos separately, because they turn out to work pretty differently.

Decided in 2024	Houses	Condominiums
Appeals decided	133,526	217,670
Got a reduction	25,879	41,243
Success rate	19.4%	18.9%
Typical cut when they won	6.5%	8.6%

And what surprised us a bit is that condos are the bigger category by a long way, and there are more condo appeals than house appeals in Cook County every single year. Both success rates land within half a percentage point of each other, which is a pretty decent sign that both numbers are measuring something real rather than just being an artifact of how we counted them.

In Illinois you win by showing that similar homes are assessed lower

So the winning argument in Illinois is uniformity, which just means showing that homes genuinely like yours are assessed lower than yours is. We read 41 residential decisions from the Illinois Property Tax Appeal Board, and 29 of them were uniformity cases, while only 6 even mentioned comparable sales.

Now that's backwards from most states, where you appeal by arguing about market value, which basically just means showing what homes like yours have recently sold for. And in a state like Washington, comparing your assessment to your neighbor's assessment isn't even allowed as evidence.

What the Illinois board wants is documentation of the assessments of not less than three comparable properties, showing the similarity, proximity and lack of distinguishing characteristics compared to your own property.

Then they decide the case with a bit of arithmetic that's honestly easier to follow than you'd expect. They take the best comparables from both sides, work out what each one's assessed per square foot of living area, and then ask where you fall in that range. In one decision it reads almost like a spreadsheet, where the comparables ran from $12.12 to $12.57 per square foot, and the subject at $12.05 fell below that range, so there was no reduction.

If you own a condo, the county never assessed your unit

Now Cook County decided 217,670 condo appeals last year, and the argument most condo owners reach for, that the unit down the hall is assessed lower than theirs, can't work here.

Cook County doesn't actually assess your condo unit. What they do is assess your whole building as one thing, and then divide that value up among the units by each unit's declared share of ownership, which comes straight out of your building's condominium declaration.

So we checked this against the county's own records for a real Chicago building. Here's every unit's assessment divided by its ownership share:

Unit	Share of building	Assessed value	Implied building value
001	14.05%	$32,801	$233,459
002	11.28%	$26,334	$233,457
005	7.00%	$16,342	$233,457
010	5.56%	$12,981	$233,471

Basically it's the same building value every single time, give or take a bit of rounding.

Which means the county never set your neighbor's number independently in the first place. They took one building value and applied a different ownership share to it, which means there just isn't anything unfair hiding in there for you to find.

Fortunately, the comparison that can work for a condo is between your building and other condo buildings. And there's a pretty neat bit of arithmetic here, because your assessment is the building's value times your share, and your floor area is the building's area times roughly that same share, so the share just cancels out. Which means your cost per square foot is simply your building's cost per square foot, and the real question is whether your building's assessed higher than comparable buildings nearby.

Also, something to keep in mind is that because the building's assessed as one thing, an appeal that succeeds usually helps every unit in it, not just yours. So if your building has an association, it's often quite a bit stronger to appeal together than to go it alone.

Winning in the right year is worth three times as much

Cook County reassesses every township on a three year cycle, which means your township gets a new assessed value once every three years and keeps it in between.

The Assessor's own guidance says that if an appeal's granted and nothing about the property changes, that value stays your assessed value until the next reassessment. So we went and tested whether that actually holds up. We took 120 Evanston houses that won a reduction back in 2022, which was Evanston's reassessment year, and then looked at what happened to them in 2023 and 2024.

And of the 90 with complete records, all 90 of them kept the reduction. Not a single one went back up. The reduced figure just repeats, right down to the dollar:

First mailed 2022	After appeal	2023	2024
$73,000	$65,249	$65,249	$65,249
$52,000	$48,770	$48,770	$48,770
$66,000	$62,256	$62,256	$62,256

So ultimately, a win in your reassessment year is worth roughly three years of savings, while a win in the last year of the cycle is only worth one. Which is about a three times difference, for exactly the same amount of effort on your part.

What loses, from the decisions themselves

Five mistakes come up over and over in the board's own reasoning.

• Comparables that aren't really comparable. The board discounts properties that are less similar in age, dwelling size or amenities, and in one case they rejected a side's evidence outright as unadjusted raw data on properties with dissimilar square footage, amenities and locations.
• Fewer than three comparables. The rule says not less than three, so one neighbor on its own isn't going to carry it.
• Comparables that are too far away. Proximity is named right in the rule itself, and boards tend to favor properties on the same block or within about a quarter mile.
• For condos, comparing yourself to another unit in your own building. Covered above, and it's the one we'd most want a condo owner to avoid wasting an appeal on.
• The size of your increase, or the size of your tax bill. Neither one is evidence about whether your assessment is uniform, so neither carries any weight at all.

But one thing that does work, and it's honestly pretty easy, is that if the county's record of your property is just plain wrong, you should correct it. Your square footage drives the whole calculation, so if that figure's off, then everything built on top of it is off too. And it's also the easiest kind of correction for a board to make, because there's nothing subjective in there to argue about.

So is it worth appealing?

Well honestly, for a lot of people, no. We'd much rather just say that plainly than have you spend an afternoon finding it out the hard way.

If your assessment already sits inside the normal range for genuinely similar properties near you, then a board's going to look at those same numbers and change nothing. And that isn't really a reflection on how well you argue it, it's just what the evidence says.

But if your building or your home is assessed above that range, then filing is free, the whole process is designed for people to do it themselves, and in your reassessment year a win holds for three years. So in that situation it's a pretty easy yes.

The only work is figuring out which of those two situations you're actually in, and that's what our free check does. It reads Cook County's own records, finds genuinely comparable properties in your assessment neighborhood, runs the same per square foot comparison the board runs, and then tells you straight which side of the line you're on. And most people who use it get told not to bother.

Check your property, free