How to Find Comps for a Property Tax Appeal (and What Actually Counts as Comparable)

by Brian Wittman

A comp is a property enough like yours that a stranger would price the two the same way. For a tax appeal you generally want at least four of them, they come from your county's own property records rather than a real estate website, and pulling them costs nothing but your evening.

That last part matters, because most of what you will find when you search this question is a company offering to do it for a share of your savings.

I appealed my own assessment after it jumped about 25 percent and the valuation came down somewhere in the range of 18 to 20 percent. I have since helped a client do the same. The comps were the part that took the longest and the part that actually won it, and nothing about the process required a professional.

This article is the method. Your county's calendar and its specific filing rules live in the county article: Cook County, Will County, and Kankakee County each run different clocks.

What counts as a comparable property in a tax appeal?

A comp has to be close to your house on the things an assessor uses to value it, not the things you happen to like about it.

The factors that matter:

Style. A split level compares to a split level. A ranch does not compare well to a two story, even at the same square footage, because the assessor's model treats them differently.

Size. Gross living area, within a reasonable band. A 1,400 square foot house is not comparable to a 2,200 square foot house on the same street.

Age. Year built, or an effective age if the house has been substantially rebuilt.

Quality and condition. The assessor's own grade for construction quality is on the property record card. Use their grade, not your opinion of it.

Proximity. Same subdivision is ideal. Same township matters more than most people realize, because the township assessor is the one who set your number and comparisons across township lines invite an argument you do not need.

Recency. Sales within the prior three years, with the most recent carrying the most weight.

The single most useful filter is same subdivision and same township. If you can find four houses that match yours on style, size and age inside your own subdivision, you have a stronger case than someone with eight scattered comps across a county.

Will County's rules put it in one sentence worth memorizing: the best comparable properties are the ones that require the fewest adjustments. If you find yourself writing a paragraph to explain why a house counts, it probably does not.

One more filter people miss: the sale has to be an arm's length transaction. Will County specifically excludes properties that were never advertised for sale, sales between related parties, sales of partial interests, court-ordered and condemnation sales, purchase options, trades, sale-leasebacks, and long-term contracts. Your neighbor selling to his daughter is not a comp.

Short sales and post-foreclosure sales, on the other hand, are generally accepted as market transactions, which surprises people. If one of those is genuinely comparable to your house, you can use it.

How many comps do you need?

More than you think, and the safe answer is to submit to the higher standard rather than the minimum.

At least three, and the number is the least important part of the answer.

Will County's Board of Review requires a minimum of three comparables, and it is three whether you are arguing overvaluation or arguing that similar homes are assessed lower. Check your own county's published rules, because that number is theirs to set.

Here is the part that actually loses appeals. In Will County, comparables have to be submitted with the original complaint. Properties offered in testimony that were not filed ahead of the hearing will not be considered at all. You cannot walk in with a folder and hand it over. If it is not filed, it does not exist.

So the real answer to how many is: more than the minimum, and all of them before the deadline. Four to six well chosen comps beat ten weak ones and beat three filed late by an infinite margin. A board member is reading a stack of these on a fifteen minute residential hearing schedule. Give them four houses that are obviously like yours and the case makes itself.

Where do you actually find comps?

Your county's own property records, searched by PIN or address. Not a real estate website.

The county maintains a record for every parcel, and that record is the same document the board is reading. It carries the assessed value, the characteristics the assessor has on file, the class code, and the sale history.

Before you start doing it by hand, check whether your county gives you a tool. Some assessors publish a comparable properties search that filters automatically on the county's own groupings, class code, square footage and age, and a few build one directly into the online appeal application. Others give you nothing but a parcel lookup and you pull record cards one at a time. It is worth five minutes on your assessor's site to find out which kind you are dealing with, because the tool version turns an evening into twenty minutes.

Also worth knowing: a county's tax portal and its assessment records are often two different systems. The portal is usually built for tax history, exemptions and deeds. It frequently will not find sales comparables for you at all.

Either way, pull the record card for your own parcel first, because you may find the error there before you ever look at a comp. Assessors carry wrong square footage, wrong bedroom counts, and finished basements that were never finished more often than you would expect.

Two things to collect for every comp: the PIN and the assessed value, and the characteristics that prove it is comparable. A comp without its PIN is not evidence, it is an anecdote.

What is the difference between an equity appeal and an overvaluation appeal?

They are two different complaints with two different standards of proof, and the comps you pull are the same either way.

Overvaluation says your assessed value implies your house is worth more than it would actually sell for. In Will County the burden is a preponderance of the evidence, which is the ordinary civil standard. More likely than not.

Equity says your house is assessed at a higher level than comparable properties, regardless of what any of them would sell for. Here the burden is clear and convincing evidence, which is a materially higher bar.

I want to be straight about that, because plenty of guidance online calls equity the easier play. Will County's own rules set a tougher standard for it. What equity gives you is that you do not have to prove what your house is worth, only that similar homes were treated differently. What it costs you is a harder standard to clear once you are there.

Equity also has a geographic limit that overvaluation does not. In Will County, comparables from outside the county will not be considered for an equity complaint under any circumstances. Overvaluation comps can sit farther away, but you carry the burden of proving they were the most comparable ones available.

The working number for equity is assessed value per square foot of gross living area. Divide each comp's assessed value by its living area, do the same for yours, and see where you land. You are showing the board a gap in how the same yardstick was applied.

And there is a third complaint basis nobody mentions. If the assessor's record card is simply wrong about your house, that is its own complaint, filed on a discrepancy in physical data rather than on comps. It requires the record card, a statement of what is wrong, and competent evidence such as a plat of survey, photographs, or construction documents. Check the card before you spend an evening on comparables.

If your house assesses at meaningfully more per square foot than four similar houses nearby, you have the argument, and you did not have to hire anyone to make it.

Why is a Zestimate not evidence?

Because an automated valuation is a model's guess about a house it has never seen, and the board knows that.

Automated estimates from real estate sites are built to be directionally useful to a shopper. They are not built to be evidence, they do not use the assessor's characteristics, and submitting one signals that you did not do the work. Boards see them constantly.

The same goes for a printout of active listings. A listing price is what someone hopes to get. An assessment argument runs on what properties actually are and what they actually sold for.

The distinction that matters is valuation versus sale data, and Will County's rules draw it clearly.

MLS listings showing sale price, sale date, descriptive data and a photograph of a comparable house are explicitly acceptable evidence. So finding sales on a real estate site is fine. That is data.

What gets discounted is the opinion of value. Will County's rules say appraisals and value opinions, including those developed and offered by internet firms, are given minimal emphasis unless certified in writing by the person who developed them. An automated estimate has nobody certifying anything.

So use those sites to find the sale. Pull the assessed value, the class code and the characteristics from the county, because those are the numbers the board is working from. Just never submit the estimate itself as your argument.

What if you do not want to do this yourself?

There are three honest options and most people only hear about one.

Do it yourself. Everything above. It costs an evening and the filing itself is free. For a straightforward residential case in a subdivision with plenty of similar houses, this is genuinely the whole job.

Hire a service. There is an industry of companies that will file for you, generally in exchange for a share of your first year of savings. They are not doing anything you cannot do, and the arithmetic is worth running before you sign: a percentage of a multi year reduction is a real number. I am not naming or recommending any of them, and I do not take a referral fee from any of them, which is why I can tell you plainly what they are.

Ask a broker to pull the comps. This is the option almost nobody mentions, and it is the one I actually offer. Pulling comparable properties is something I do every week. If you want a set of comps for your parcel, ask and I will pull them. There is no fee and no obligation, and you file it yourself.

I would rather you win your appeal and remember who helped than take a cut of it.

The Bottom Line

A comp is a house enough like yours that the assessor's own records show the two should be valued the same way. Match on style, size, age, quality and proximity, stay inside your township and ideally your subdivision, pull everything from the county's records by PIN, and bring more than the minimum.

Run the equity argument on assessed value per square foot. It is easier to prove and harder to argue with than a claim about market value.

And skip the Zestimate. It is the fastest way to tell a board you did not do the work.

If you want comps pulled for your address, or you want someone to look at whether your case is worth filing at all, reach out. That is free, and it is the useful version of everything above.

Frequently Asked Questions

What is a comparable property for a property tax appeal?

A property similar enough to yours on the characteristics the assessor uses that the two should carry similar assessments. The factors are style, gross living area, year built, construction quality and condition, and proximity, with same subdivision and same township being the strongest match. Sales within the prior three years carry the most weight.

How many comps do I need for a property tax appeal?

Will County requires a minimum of three, for either complaint basis, and other counties set their own. Bring four to six anyway, because well matched comps are more persuasive than a bare minimum. The more important rule is timing: in Will County, comparables must be submitted with the original complaint, and properties offered in testimony that were not filed ahead of the hearing will not be considered at all.

Where do I find comps for a property tax appeal?

Your county's online property search, using the PIN. That record carries the assessed value, the characteristics on file, and the sale history, and it is the same document the Board of Review is reading. Pull your own parcel's record card first, since assessors sometimes carry wrong square footage or an incorrectly finished basement.

Can I use Zillow for a property tax appeal?

You can use it to find recent sales, but not as your evidence. MLS listings showing sale price, sale date, descriptive data and a photo of a comparable house are explicitly acceptable in Will County. What gets discounted is the opinion of value: the rules give minimal emphasis to appraisals and value opinions, including those from internet firms, unless certified in writing by whoever developed them. An automated estimate has nobody certifying it.

What is the difference between an equity appeal and a market value appeal?

An overvaluation appeal argues your assessment exceeds what the house would sell for. An equity appeal argues your house is assessed at a higher level than comparable homes, whatever any of them would sell for. They carry different burdens of proof: in Will County, overvaluation requires a preponderance of the evidence while equity requires clear and convincing evidence, which is the higher standard. Equity also will not accept comparables from outside the county.

Can someone pull comps for me?

Yes, and it does not have to cost you a percentage of your savings. Companies will file the whole appeal for a share of the first year's reduction. A broker can also pull comparable properties for your parcel at no cost, which is what I do when someone asks. You still file it yourself.

Brian Wittman is a licensed real estate broker (Real Broker LLC), mortgage loan originator (NMLS #2646598, NEXA Mortgage, LLC, Equal Housing Lender), and life insurance producer (Levinson & Associates). This article is for educational purposes only and is not financial, lending, tax, or legal advice, an offer, or a commitment to lend; all loans are subject to credit approval. Information is accurate as of the publication date; for current details and full disclosures, visit https://bluejeanbroker.com/disclosures.