Last year, a homeowner in the Chicago suburbs opened her assessment notice and found her house valued $60,000 above what she'd paid for it eight months earlier. She paid it. Most people do. My guess is she never compared her number to the four houses on her block that are the same age, size, and style as hers, which is exactly where the crack in the system usually shows up.
Assessment notices read like utility bills. A number, a deadline, a total you owe. That flat presentation tricks you into treating the figure as a fact rather than an opinion, which is all it really is. Your assessor made an estimate based on mass data, and mass data gets things wrong constantly. Here's how to check the math on your own notice, what to look for, and when to bring in professional help.
What Your Assessor Is Actually Guessing At
Your local assessor isn't appraising your house the way a realtor would. They're running you through a mass valuation model alongside thousands of other parcels, using square footage, age, construction type, and recent neighborhood sales. The approach is efficient and, for most properties, roughly accurate. For your specific house, it can be wildly wrong.
Two numbers on your notice deserve a hard look before anything else. The first is your assessed value. The second is your equalization factor, sometimes called the multiplier, which adjusts local assessments to bring them in line with statewide sale prices. Counties publish this figure annually, and in Illinois the state government publishes the multiplier your county applies. If your county's multiplier jumped this year, part of your higher bill has nothing to do with your house.
I'd start by pulling the notice from last year and placing it next to this one. Look for changes in the physical description fields, not just the value. Assessors update their records in bulk, and data entry errors get baked in quietly.
The Four Grounds That Most Appeals Rest On
Appeals aren't won by arguing that taxes are too high in general. They're won by pointing to a specific defect in how your number was calculated. In practice, most successful appeals lean on one of these:
Lack of uniformity. Your house is compared against comparable properties and you're paying more than they are without a reason for it.
Overvaluation. The assessor's market value exceeds what your property would actually sell for in an arm's length transaction.
Description errors. Wrong square footage, wrong bedroom count, a finished basement that doesn't exist, a garage that was never built.
Uninhabitable condition. Major reconstruction, fire or flood damage, or code violations that make the property unusable during the assessment period.
Notice that "my taxes went up" is not on that list. Increases happen to everyone in a reassessment year, and the appeal board hears the same complaint hundreds of times. Specificity is what separates a filing that gets reviewed from one that gets stamped.
How Do You Find Your True Comparables?
Comparable sales are the backbone of any defensible appeal, and most owners pick them badly. They choose the nicest house on the street or the one that sold highest, then get confused when the board rejects the comparison.
You want three to five properties that match yours on the things assessors weight heavily: square footage within a couple hundred feet, similar lot size, same construction type, built in the same era. A ranch and a two story colonial aren't comparable even if they sit twenty feet apart. Pull recent sale prices from your county recorder's online records, and check the assessed values of those same properties in the assessor's public database. If your neighbor's nearly identical house is assessed 20 percent lower, you've found something the board will actually read.
Worth knowing the broader picture too. Homeownership rates and housing patterns vary a lot across regions, and the Census Bureau publishes housing data that shows how differently markets behave from one metro to the next. That context won't win your appeal alone, but it helps you judge whether your valuation narrative holds up.
A Practical Checklist Before You File
Work through this in order. It takes an afternoon and saves you from a filing that gets bounced on a technicality.
Confirm your appeal deadline. The assessor's office sets the first one, and it's usually short.
Request your property record card from the assessor. This shows every data point they used on your house.
Walk your own property against that card. Measure rooms. Count bathrooms. Check the basement classification.
Photograph anything that contradicts the record: water damage, a missing structure, an unpermitted addition you tore out.
Pull assessed values for three to five true comparables from public records.
Write your argument in one paragraph, tied to one of the four grounds above.
Submit before the deadline and keep a copy of everything.
If you miss the assessor's deadline, you're not finished. Most counties have a second window at the board of review, and filing there is standard practice, not a last resort.
When to Hand It Off
Filing an appeal yourself is completely doable for a valuation dispute. Where it gets tangled is uniformity cases, income producing properties, and commercial buildings, because the analysis requires pulling assessment ratios across dozens of parcels and building an argument the board recognizes. That's the kind of work property tax advisors do all day, and the fee structure usually ties their compensation to whatever savings they recover, which tells you something about how confident they are in the outcome.
My honest take: if your property is a standard single family home and you've found a clear description error, do it yourself. If you're looking at a strip mall, an apartment building, or a uniformity claim with no obvious paper trail, the hours you'd burn learning the process cost more than the professional fee. Property tax appeals are one of the few areas where paying someone to do the work often pencils out.
The bigger point is that an assessment notice is a starting position, not a final bill. According to the Bureau of Labor Statistics, property taxes represent a significant and growing share of household housing costs, which is exactly why so few owners push back. The system counts on that. Pull your notice off the pile this week. Compare it to last year's, check the square footage, look up two neighbors, and put the deadline on your calendar. You might find nothing, and that's a fine outcome. You might find $60,000 of someone else's error sitting on your bill.
Copyright © 2026 California Business Journal. All Rights Reserved.
For California Business Journal Disclaimers, go to https://calbizjournal.com/terms-conditions/.
