5,782 Thornton Township homeowners took an appeal to a decision in 2024, and 1,090 of them got a reduction. That's 18.9 percent. Here's what the county's own records say about your odds, your deadlines, and the argument that actually wins in Illinois.
So Cook County gives you two separate free appeals on the same assessment, at two different offices. The Assessor goes first, and the Board of Review opens its own window afterwards in a different building. It takes the same evidence, and its evidence deadline falls ten days after the filing deadline, so if you're short of time you can file first and send the evidence after that.
In most states you'd appeal by arguing about market value, showing what homes like yours have recently sold for. Illinois works the other way round. The winning argument here is uniformity, which basically 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.
And what the 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. Then it works out what each one's assessed per square foot of living area and asks where you fall in that range. Above the range is the case boards grant, and that's the whole test. If you're inside it or below it, then honestly no amount of paperwork is going to change the answer.
So that sits pretty close to the county as a whole, where 19.4 percent of house appeals won. Across all 38 townships the rate runs from 9.2 to 30.2 percent, so where you live really does change your odds.
Now Cook County reassesses every township on a three year cycle, and the Assessor's own guidance says that if an appeal's granted and nothing about the property changes, that value stays put until the next reassessment. So we tested it against 120 Evanston houses that won back in 2022, and of the 90 with complete records all 90 kept the reduction, right down to the dollar.
Which means a win in Thornton right now holds for roughly 4 years before 2029 resets it. Winning early in a cycle is worth about three times as much as winning at the end, and that's for exactly the same afternoon of work.
Thornton only decided 145 condo appeals in 2024, which honestly isn't enough to give you a win rate worth trusting. So we're not going to make one up.
Because Cook County doesn't assess your condo unit at all. What they do is assess the whole building as one thing, then divide that value among the units by each one's declared share of ownership, straight out of your condominium declaration. So the argument most condo owners reach for, that the unit down the hall is assessed lower than theirs, can't really work here, because the county never set that neighbor's number independently in the first place. Fortunately, the comparison that does work is between your building and other condo buildings.
For a lot of people the answer is no, and we'd rather say that plainly than have you find it out the hard way. Even here, about 81 out of every 100 appeals didn't produce any change at all.
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. But if you're above that range then filing's free, the whole process is built for people to do it themselves, and a win early in your cycle holds for years.
So really the only work is figuring out which of those two you're 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 Thornton home, free
Every win rate and cut size here comes from the Cook County Assessor's published appeals dataset for tax year 2024, counting cases where the certified value came in below the mailed value. Houses are classes 202 through 210, 234 and 278. Condominiums are class 299.
And the decision rule and the quoted standard come from decisions of the Illinois Property Tax Appeal Board at ptab.illinois.gov, which we read in full. The uniformity requirement is 86 Illinois Administrative Code 1910.63(e). The appeal windows come from the Assessor's own calendar and the Board of Review's published schedule.
If you spot an error in any of this, please write to hello@propertytaxbuddy.com and we'll correct it and say what changed.