How Do You Appeal Your Property Tax Assessment in Kendall or Kane County?
You file a property tax appeal with your county’s Board of Review, not with your township assessor or the county treasurer. In Kendall County you have 30 days from the date your township publishes its assessment notice; in Kane County you have 30 calendar days from publication of the assessment list, and the Board only accepts paper filings by mail or in person. Every appeal needs at least three comparable properties or recent sales data attached, because a complaint with no evidence rarely moves an assessed value. Miss the window, skip the comparables, or argue the wrong number, and the reduction you were counting on doesn’t happen this year.
By Kealan O’Neil | September 24, 2026
If you’re in the middle of a sale right now, this isn’t the same question as how property taxes get prorated at closing, proration splits a bill that’s already set. A property tax appeal is about changing the number before it’s set, and it’s one of the most searched real estate questions in Kendall and Kane County every fall, for good reason: a dozen-plus paid appeal services are already bidding on it, which tells you how many local owners think they’re over-assessed. Here are the three mistakes that sink a property tax appeal before it ever gets a fair look.
The 30-Day Window Most Owners Miss
Kendall County has nine townships, and each one publishes its own assessment notices on its own schedule, not all at once and not printed on your tax bill. Kendall County’s assessments office confirms the rule that governs every property tax appeal filed in the county: you have 30 days from the date your township publishes its assessment list to file with the Kendall County Board of Review at 504 S. Main St. in Yorkville. Miss that window and the Board can’t accept your complaint, no matter how strong your case is.
Kane County runs on the same 30-day clock, measured from publication of that year’s assessment list, but the Kane County Board of Review’s rules add a wrinkle a lot of owners don’t expect: the Board only takes paper filings, delivered in person or by mail to its office in Geneva. Fax and email submissions are rejected outright, and overnight express doesn’t count as filing in person. If you’re planning to mail a property tax appeal in Kane County on the last possible day, plan for it to actually arrive by the deadline, not just get postmarked.
The fix is simple. Watch for your township’s assessment publication every year, write down the date it posts, and count 30 days from there, not from whenever you happen to open your tax bill months later.
Kendall County’s guidance also points to a faster first step before you file anything formal: call your township assessor and ask them to walk through how your assessment was calculated. Sometimes that conversation turns up a data error (wrong square footage, a basement counted as finished when it isn’t, a garage that was never built) that gets corrected without a formal property tax appeal at all. If the assessor’s office confirms the number is correct, or you still disagree after that call, that’s when you file with the Board of Review before your 30 days run out.
Why an Opinion Isn’t Evidence
“My taxes are too high” is not a property tax appeal. Both counties want numbers, not a feeling.
Kendall County requires a Residential Grid Sheet with every appeal: a minimum of three comparable properties, matched on lot size, structure type, year built, living area, and basement, with their sale dates, sale prices, and current assessments listed side by side. For this year’s cycle, comparable sales have to fall between January 1, 2025, and July 1, 2026, to count as evidence. Skip the grid sheet and the Board has nothing to measure your assessment against.
Kane County is stricter still. If you’re arguing your home is overvalued, you need at least three comparables similar in size, age, construction quality, and condition, with sales from the last two to three years, or a licensed Illinois appraiser’s opinion of value as of January 1, 2026. If you’re arguing your assessment is out of line with similar homes nearby (an equity or uniformity appeal), your comparables have to come from Kane County itself. And however you argue it, your evidence has to reach the Board within 14 calendar days of the filing deadline, not whenever you get around to it.
If you bought your home recently, in either county, a straightforward purchase price and closing date can carry real weight in a property tax appeal, as long as you can document it was an arm’s-length sale and not a transfer between family members or an estate settlement.
Assessed Value vs. Fair Market Value
Illinois assesses property outside Cook County at one-third of fair market value, so the number on your tax bill isn’t what the county thinks your home is worth. It’s roughly a third of that. Both Kendall and Kane County’s appeal forms ask for your opinion of fair market value, then divide it by three to calculate your proposed assessment.
This is where more property tax appeal filers go wrong than anywhere else. If your home is worth $400,000 and you look at the assessed value on your bill (something closer to $133,000) and assume you’re being taxed as if the county valued your home at the assessed figure, you’ll either file an appeal you don’t need or argue for a fair market value that’s already too low to help you. Before you file a property tax appeal, check your township’s fair cash value estimate against actual closed sales in your subdivision, not just against the number printed on your bill.
This is exactly where an agent’s access to real, recent comparable sales beats a generic online appeal service that’s never set foot in your neighborhood. I walk clients through this constantly, especially when a reassessment doesn’t match what their home actually sold for, or would sell for today.
It also matters if you’re buying, not just if you already own. Before you close on a resale home in Yorkville, Oswego, Montgomery, or anywhere else in Kendall or Kane County, it’s worth pulling the current assessment and checking whether it’s in line with recent comparable sales in that subdivision. If it isn’t, you may be inheriting an appeal opportunity the current owner never took, or a reassessment that’s about to catch up once your sale price shows up in the county’s records.
What Happens After You File
If the Board of Review’s decision doesn’t match what your comparables support, you’re not done. Decisions from either county’s Board can be appealed further to the Illinois Property Tax Appeal Board, or to circuit court, though PTAB has its own filing deadline (30 days from the Board’s decision) and its own evidence rules. Kane County also gives residential filers a choice at the Board of Review stage: a standard hearing by teleconference where you argue your case out loud, or a streamlined hearing where you submit your evidence in writing and skip the appearance.
One more thing worth knowing if you closed on a newly built home in the Fox Valley in the last year or two: your first tax bill is often based on unimproved land, and the reassessment that follows once the county catches up to the finished home’s value can be its own kind of surprise, separate from anything a property tax appeal addresses. And if the home sits inside a special service area, that SSA charge is a separate tax line altogether that a property tax appeal doesn’t touch, because it isn’t based on your assessed value at all.
Common Questions About Property Tax Appeals in Kendall and Kane County
Owners weighing whether to file usually ask some version of these.
How much does it cost to file a property tax appeal in Kendall or Kane County?
Do I need a lawyer to file a property tax appeal in Illinois?
What happens if I miss the 30-day deadline for my Kendall or Kane County property tax appeal?
Will winning a property tax appeal lower my tax bill right away?
Should I check for a property tax appeal history before buying a home in Kendall or Kane County?
Whether you’re in Kendall County or Kane County, a property tax appeal comes down to three things: hitting the 30-day window, filing real comparable evidence, and arguing the right number. Get any one of those wrong and the Board has no way to lower your assessment, even when your instinct that you’re over-assessed turns out to be correct.
If you’re weighing whether your Yorkville, Oswego, Montgomery, or wider Fox Valley home is over-assessed, I can pull the actual comparable sales your property tax appeal needs, the same data I use when I’m pricing a listing or helping a buyer make an offer. Call or text Kealan at 630-425-8815.
About Kealan O’Neil
Kealan O’Neil is the Designated Managing Broker and founder of O’Neil Property Group, an independent real estate brokerage based in Yorkville, Illinois. He and his team help buyers and sellers in Yorkville, Oswego, Montgomery, and the surrounding Kendall and Kane County communities, and he owns and manages a local rental portfolio, so he approaches every decision as both a broker and an investor. Call or text Kealan at 630-425-8815.
This post is general information about real estate in the Fox Valley, not legal, tax, or financial advice. Real estate laws, tax rules, and municipal ordinances change, and how they apply depends on your specific situation. Talk with a licensed attorney, CPA, or lender before making decisions about a purchase, sale, or tax matter. O’Neil Property Group is a licensed Illinois real estate brokerage.