Why Is Your Neighbor Paying Less Property Tax on the Same House?
Updated June 18, 2026
Two nearly identical houses sit on the same block. Same size, same age, same condition. One owner pays hundreds, sometimes thousands, more in property tax every year than the other. It's one of the most common frustrations I hear from Cook County homeowners, and if you've compared your bill to a neighbor's and wondered why yours is higher, you're not imagining it.
Here's why it happens. The Assessor values hundreds of thousands of properties at once, by formula, and nobody walks through your home before a number gets attached to it. Uneven results aren't rare exceptions in a system like that. They're baked in. But an assessment isn't the final word, and the gap between your home and a similar one down the block is often the very evidence that wins an appeal.
Below, I'll walk through why two similar homes get assessed so differently, how to tell whether yours is overassessed, and what I can actually do about it as a Cook County property tax attorney.
How Two Identical Homes End Up Assessed Differently
The differences almost never come from the houses themselves. They come from how each home gets valued, recorded, exempted, and appealed over the years. These are the usual culprits.
- Different comparable sales and timing. Your assessment leans heavily on recent sales of comparable homes near you, and the words "recent" and "comparable" carry a lot of weight. If one home got valued off sales from a hot stretch of the market and the other off a slower period, the two numbers can drift far apart even when the houses are twins. The county reassesses on a three-year cycle, township by township, so timing alone can put you and your neighbor in different worlds.
- Mis-coded classifications and small record differences. This is where a lot of the unfair gaps hide, and it's the kind of thing homeowners almost never catch on their own. How your property is classified and recorded drives the number. A difference as small as 10 square feet of recorded living area can bump a property into a different class. A home on the books as masonry can be assessed higher than an identical neighbor recorded as frame or siding, even when the real difference is nothing. None of that reflects what your home is actually worth, and when the record is wrong, you're the one paying for it.
- Overstated square footage and other record errors. The errors that actually move the needle are the substantive ones: overstated square footage, a mis-coded classification, a lot size that doesn't match the plat. If the records say your home is 2,000 square feet and it's really 1,600, you're being taxed on space you don't have. Pull your record on the Assessor's website and read it line by line against your actual home. Anything overstated is a concrete, provable basis to appeal.
- Exemptions one owner claimed and the other missed. Two homes can carry the same assessed value and still produce very different bills, simply because one owner claims exemptions and the other doesn't. The Homeowner Exemption is the one people miss most. It often drops off when a property changes hands, and plenty of new owners never knew it was there. Seniors miss the Senior Exemption the same way. When your neighbor claims exemptions you don't, the gap shows up on the bill rather than the assessment. The good part is that missed exemptions are usually recoverable. Through a Certificate of Error I typically see clients get back somewhere around $700 to $1,000 a year, often going back three or four years. (See our full guide to Cook County homeowner exemptions for what you may qualify for and how to claim it.)
- One neighbor appealed and the other did not. A successful appeal lowers your assessment for that cycle. If your neighbor appealed and you never did, the two values drift apart over the years, not because anything about the houses changed, but because one of you acted. There's a knock-on effect too. The more people in an area appeal and win, the more good comparables exist for the next owner to lean on. When nobody appeals, that pool dries up.
- Different Assessor neighborhoods. Two homes directly across the street from each other can fall into different official Assessor neighborhoods. When that happens, each one gets valued off a different set of comparable sales. You'd never see the boundary from your front porch, but it can swing the number.
How Cook County Assessment Actually Works
A little math helps here. For a home, your assessed value is 10% of the market value the Assessor assigns it. The State of Illinois applies an equalization factor (the "state multiplier") to get your Equalized Assessed Value, or EAV. Your exemptions come off the EAV, the local tax rate applies to what's left, and that's your bill.
Everything starts with that one estimate of market value. Get it too high, and every number below it is too high. If you want the full breakdown, I've covered how your bill is calculated separately.
One thing blindsides new buyers constantly. Pay a strong price in today's tight market, and the Assessor often raises your assessment the next year to at or just below what you paid. What you paid isn't necessarily what the place is worth, but a recent sale is the strongest evidence the Assessor has, so they use it. Worse, the tax figure you saw at closing was a year behind, so the jump feels like it comes out of nowhere.
How to Check Whether You Are Overassessed
There are two separate ways to challenge an assessment, and the strongest appeals use both. I tell clients not to put all their eggs in one basket. The analysts are people, and they weigh arguments differently. One approach can land where the other falls flat.
1. The uniformity argument (assessed-value comparison)
Find similar homes near you assessed for less than yours. This is the "why is my neighbor paying less" question turned into evidence. The catch is that the comparables have to be real. Two things matter more than anything else: the class and the neighborhood code. A home in a different class, or a different Assessor neighborhood, isn't a valid comp no matter how much it looks like yours. It has to be apples to apples, and within apples, Granny Smith to Granny Smith, not Granny Smith to Honeycrisp. Clients bring me comps all the time that feel right and fall apart on exactly those two points.
2. The market-value argument (recent sales)
Find recent sales of genuinely comparable homes that went for less than your assessed market value. Comparability is everything again: similar square footage, lot size, age, condition, same class, same neighborhood. A licensed appraisal carries real weight here, especially on unusual or higher-value properties.
Say your home is assessed at $300,000 and three genuinely similar homes nearby just sold around $250,000, or sit well below you on assessed value. That's grounds to appeal on one or both theories. For what actually persuades an analyst, see the role of evidence in a property tax appeal.
Why a Fair Assessment Matters Beyond One Year's Bill
An overassessment isn't a one-year problem. With a three-year reassessment cycle, an inflated value keeps costing you until you fix it. Even a $500 gap a year is $5,000 over a decade.
And it reaches past the tax bill:
- Refinancing. Lenders look at your tax record, and an inflated bill makes your monthly costs look higher than they are, which can cost you on rate and terms.
- Selling. Buyers compare taxes when they make offers. A home with unusually high taxes for the block can sit longer or sell for less.
- Home equity. A fair number keeps the picture of your biggest asset honest.
There's a fairness piece I care about here too. In lower-value neighborhoods, effective tax rates often run much higher than in wealthy ones, so a modest reduction can mean far more to a family's budget, and those are exactly the owners least likely to appeal. I wrote more about that in why low-income homeowners rarely appeal, and how to change it.
Don't Wait: The Appeal Window Is Short and Easy to Miss
This is the trap that catches almost everyone. By the time the bill lands, the window to appeal that assessment has usually closed. Your bill reflects a tax year that was assessed and reviewed months earlier. The Assessor and the Board of Review run on different schedules, each township has its own short window, and most people aren't checking those calendars. So they find out too late, once the bill or a jump in their mortgage escrow shows up.
So don't wait for the bill. Track the Assessor's and Board of Review's calendars for your township, or have someone track them for you. You can check your township's appeal deadline by address or PIN in seconds. Appeal when you're right and you've protected yourself. Do nothing, and the only person to blame is the one who missed the deadline.
A denial at the Assessor level isn't the end. The Board of Review is independent, and I've had plenty of cases that didn't land at one office and won at the next. See your options after a denial if it comes to that.
How a Property Tax Attorney Levels the Playing Field
You can file on your own, and some homeowners do. But the process runs on ordinances, deadlines, and specific evidence rules, and the most common reason a do-it-yourself appeal fails is bad comparables: comps that look fine but sit in the wrong class or neighborhood, or that actually carry a higher price per square foot than your own home.
I bring 12+ years of legal experience to this, including years as a City of Chicago administrative-law attorney. Appeals at the Assessor and the Board of Review are administrative proceedings, the same strict, ordinance-driven world I came up in. That shapes how I build a case: meet what the ordinance actually requires, bring complete and current evidence, and treat the analysts as people, not opponents.
In practice that means I re-run the comparables on every case so they're current and truly comparable, build both the uniformity and market-value arguments when the facts support them, check that your exemptions are actually in place, and stay on top of the filing and deadlines so nothing slips. For the trade-offs, see should you hire a lawyer to appeal.
Stop Overpaying While Your Neighbor Pays Less
Gaps between similar homes come from timing, record and classification errors, exemptions, past appeals, and neighborhood lines. Not one of those is a reason to accept an unfair number. My firm helps Cook County homeowners review their assessment, gather the right evidence, and file appeals that hold up.
To talk it through or set up a free consultation, visit my property tax page. There's no reason to keep overpaying while your neighbor pays less on the same house. Find out whether your assessment is fair, and do it before the window closes.
