Over tax years 2023 through 2025, one full three-year reassessment cycle, the Cook County Board of Review issued 106,423 decisions on two- to six-unit apartment buildings. It cut the value on 45.7% of them. The median cut was 7.5%, or about $3,600 of assessed value. That is $36,000 of the Assessor's market value.
Owners who filed for their own buildings did better as a group: 57.2% got a cut.
And if you live in one of the units, you can still get the homeowner exemption. In tax year 2024, 76,137 of the county's 150,218 two- to six-unit buildings carried it.
Quick Answer
Two- to six-unit buildings in Cook County are valued like houses, from sales, not from your rents. The Board of Review cut 45.7% of decisions on them over tax years 2023 to 2025, close to the 49.5% rate for houses, with a slightly larger median cut. The evidence that works is sales of similar buildings nearby, corrections to the county's record, and proof of condition. If you rent units, the Board's rules ask for rent and tax-return paperwork too. An owner who lives in the building as a principal residence can claim the homeowner exemption, and the senior exemptions if eligible.
Is your building class 2-11 or 2-12?
The Assessor's class definitions:
- Class 2-11: an apartment building with 2 to 6 units, any age.
- Class 2-12: a mixed-use building with apartments and commercial space totaling 6 units or fewer and under 20,000 square feet.
- Seven or more units fall in class 3, the multi-family class, which the Assessor handles in a separate appeal category.
Both 2-11 and 2-12 are residential classes, assessed at 10% of market value, the same as a house. The Board handles them in its residential section, which covers small apartment and mixed-use buildings with fewer than 7 units and under 20,000 square feet.
Look up your PIN on the Assessor's site and check the class and unit count first. If the county has your building in the wrong class, that is its own appeal issue. To move a building into 2-11, the Assessor's rules ask for proof that each unit is lived in and has its own entrance, mailbox and utility meters, with leases or rent rolls recommended.
How the Assessor values them
The same model as houses. The Assessor's published residential model documentation says it values classes 2-11 and 2-12 in the same countywide model as single-family homes. That model learns from past sales. It uses the number of apartments, the number of commercial units, building size, age, location and neighborhood data.
Not your rent. The model does not use a building's own rents. The Assessor's appeal rules leave residential buildings with 6 or fewer units out of its income-property requirements.
Vacancy usually doesn't count. The Assessor's vacancy policy treats 2- to 6-unit buildings as residential. For those, it recognizes vacancy only after a casualty such as a fire or flood. An empty apartment, by itself, is not grounds for a cut.
How well the values match sales
We compared the Assessor's tax year 2025 values with 4,792 arm's-length sales of two- to six-unit buildings in 2024.
- Typical level: the median value was 83.7% of the sale price, against 88.9% for houses.
- More scatter: 25.3% of these buildings had a value-to-price ratio at least 20% above the median for small apartment buildings. For houses it was 12.7%.
- Cheaper buildings sat highest: in the cheapest fifth of sales, under $270,000, the median value was 109.4% of the sale price. Leaving out sales with a company on either side, it was 95.7%. The other fifths ranged from 76% to 84%.
Cheaper buildings sold for less than the Assessor's value more often. Part of that may be condition the county's records don't show. If your building needs work, document it. The same pattern for houses is in our look at whether cheaper homes are assessed at a higher share of value.
What evidence tends to work
Sales of similar buildings. The Assessor's rules ask for at least three comparables and recommend five. Pick buildings close to yours with the same unit count, similar size, age and construction, and arm's-length sales. Two-flats should be compared with two-flats.
Your own purchase. If you bought recently, your closing papers matter. The Board's rules require you to disclose a purchase within three years of the assessment date, and the Assessor's within two. A price below the Assessor's value is strong evidence; see why your closing price is evidence.
Record errors. Check the unit count, commercial units, building square footage, age, basement and garage on the Assessor's property details. The Assessor's rules require filers to point out errors and back up corrections. Our guide to property record card errors shows where to look.
Condition. Dated photos of the outside and inside, repair estimates and inspection reports. The model sees records, not your roof.
Uniformity. The Board's guidance for owners explains how to divide the building assessment by building square footage and compare it with similar properties in your neighborhood and class. If yours is assessed higher per square foot, that is a uniformity argument. See overvaluation versus lack of uniformity.
Rent paperwork at the Board. The Board's Rule 20 says that for property that is leased or available for lease, the owner should file Schedule E from the federal return for the three years before the assessment date, plus leases or rent rolls. For buildings of 12 units or fewer, it also asks for a sworn statement about any family or business ties between landlord and tenants. The rule does not exempt small buildings. Because these buildings are valued from sales, pair any rent evidence with comparable sales.
Who can file
If the building is titled in your name, you can file yourself at both offices. The Board's FAQ says owners of their own small apartment or mixed-use building may represent themselves. A building owned by an LLC or corporation must be represented by an attorney at the Board.
County appeal filings are free.
Board of Review results
Tax years 2023 through 2025, PIN-level decisions:
| Property | Decisions | Share cut | Median cut, % of assessed value | Median cut, assessed value |
|---|---|---|---|---|
| Two- to six-unit apartments (2-11) | 106,423 | 45.7% | 7.5% | $3,609 |
| Small mixed-use (2-12) | 14,048 | 26.5% | 9.1% | $5,182 |
| Houses and townhouses | 588,741 | 49.5% | 6.7% | $2,561 |
| 2-11, owner-filed | 21,381 | 57.2% | 8.5% | $3,123 |
| 2-11, attorney-filed | 85,042 | 42.9% | 7.3% | $3,815 |
Owner-filed 2-11 appeals got a cut more often than attorney-filed ones. That doesn't prove filing yourself works better. Owners who file alone may have clearer cases.
The share of 2-11 decisions with a cut moved with the region being reassessed: 38.6% in tax year 2023, 52.6% in 2024 (Chicago's reassessment year) and 43.7% in 2025. About three in four of these decisions were in the city.
The homeowner exemption still applies
To get the homeowner exemption, the Assessor says you must own the property (or be responsible for its taxes) and live there as your principal residence on January 1. State law defines a homestead as residential property its owner lives in as a principal home. Nothing excludes a building with tenants in the other units.
The record bears that out. In tax year 2024:
- 76,137 of 150,218 class 2-11 buildings (50.7%) had the homeowner exemption. Of those, 97.6% got the standard $10,000 of equalized assessed value, the same amount as a house.
- 29,426 had the senior exemption and 12,534 had the Senior Freeze.
- For class 2-12, 2,907 of 13,884 buildings (20.9%) had the homeowner exemption.
The exemption applies to the building's PIN, not per unit. If you have lived in the building for years and the exemption is not on your bill, the Assessor's refund process (it calls it a Certificate of Error) can recover missed past years. Censum's exemption check is free.
Where Censum fits
On Censum's free appeal check you enter a PIN or address and see appeal odds and the appeal window that is open. Some two- and three-flats have more than one PIN; Censum's FAQ says to match each PIN to the tax bill, and a packet covers one PIN. Censum prepares appeal packets if you want help, and can prepare the Assessor's refund filing for missed exemptions on past years. The Board decides every appeal.
The numbers behind this article
Board results are Censum's tabulation of the Board of Review Appeal Decision History dataset (7pny-nedm), queried November 11, 2026, tax years 2023 to 2025, PIN-level decisions. Median cuts are among decisions with a cut. Houses and townhouses are classes 2-02 to 2-10, 2-34, 2-78 and 2-95. "Owner-filed" is the dataset's Individual/Pro Se filer type. "In the city" counts the eight city townships. Exemption counts are from PTAXSIM, the Cook County Assessor's Office research database (version 2024.0.0), tax year 2024 PIN records; the Assessor describes PTAXSIM results as not official. The sales comparison joins the Assessor's Parcel Sales dataset (wvhk-k5uv, 2024 sales) to its Assessed Values dataset (uzyt-m557, tax year 2025 values as first mailed), classes 2-11 and 2-12. Screens: one-parcel sales passing the dataset's own sale filters; Warranty, Trustee or Other deeds; foreclosure, court and estate deeds removed; sales with a bank or government body on either side removed; last sale per PIN; ratios more than three interquartile ranges outside the quartiles trimmed, the default rule in the Assessor's ratio-study package. "Company on either side" means LLC, Inc, Corp and similar words in the buyer or seller name.
FAQ
Is a two-flat valued on its rents?
No. The Assessor values classes 2-11 and 2-12 with its residential sales model, the same one used for houses.
Can I get the homeowner exemption if I rent out the other units?
Yes, if you own the building and live in one unit as your principal residence on January 1. In tax year 2024 about half of Cook's 2-11 buildings had it.
Does a vacant unit lower my assessment?
Usually not. The Assessor recognizes vacancy on 2- to 6-unit buildings only after a casualty such as a fire or flood.
Do I need an attorney?
Not if the building is in your name. If an LLC or corporation owns it, the Board requires an attorney.
Sources
- Cook County Assessor, Definitions for the Classifications of Real Property
- Cook County Assessor, 2026 Official Appeal Rules
- Cook County Assessor, 2026 Guidelines for Filing Appeals
- Cook County Assessor, Vacancy Policy
- Cook County Assessor, Homeowner Exemption
- Cook County Assessor, residential valuation model documentation
- Cook County Board of Review, Residential Appeals
- Cook County Board of Review, Official Rules (2025)
- Cook County Board of Review, How to Present a Case
- Cook County Board of Review, Frequently Asked Questions
- Illinois Property Tax Code, 35 ILCS 200/15-175 (general homestead exemption; definition of homestead property)
- Censum FAQ
- Censum tabulation of the Cook County Board of Review Appeal Decision History dataset, tax years 2023 to 2025.
- PTAXSIM, the Cook County Assessor's Office research database, version 2024.0.0.
- Cook County Assessor, Parcel Sales and Assessed Values datasets (Cook County open data).
Sources accessed November 11, 2026.
Next step
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Censum LLC is a data and analytics company, not a law firm and not a tax advisor. Censum is independent and is not affiliated with Cook County or any government agency.