Cook County Keeps Apartment Buildings in the Residential Class
Program and regulatory figures verified September 15, 2026. Details change; confirm your scenario with us.
On a larger building the assessment class decides a real share of the tax bill, and the tax bill sits in the denominator of your DSCR. Cook does something most people assume it does not: it keeps apartment buildings on the residential side of the line.
The two levels
The Assessor publishes a classification code that sorts every parcel. Its second part is headed residential assessment classes at a 10% level of assessment, and its third part is headed commercial and industrial assessment classes at a 25% level. Where a parcel lands is therefore worth two and a half times on the same market value.
| Class | What it covers | Level of assessment |
|---|---|---|
| Major Class 2 | Residential, including 2-11, an apartment building with two to six units, any age | 10% |
| Major Class 3 | Multi-family, including 3-91, apartment buildings over three stories with seven or more units | 10% |
| Major Class 5 | Commercial and industrial | 25% |
Cook County Assessor, Definitions for the Classifications of Real Property. Major Class 3 appears between the 10% residential heading and the commercial heading in the Assessor's own document.
Mixed use splits by use
On a mixed commercial and residential building the Assessor states that the residential portion continues to be assessed at 10% of market value and the commercial portion at 25%, based on use. A storefront with flats above is not forced wholly into either class.
This is not a discount against the rest of Illinois
It is tempting to read 10% against the 33 1/3% that applies in every other county and conclude Cook is cheap. It is not, and we would rather say so. The Department of Revenue is required to equalize among counties so that property is assessed at 33 1/3% of fair cash value, and it does that with a multiplier applied to Cook, tentatively 2.8683 for 2025. The classification advantage is real within Cook, between a residential class and a commercial one. It is not a cross-county saving. The full arithmetic is on the tax page.
Mike Certo · NMLS #260555 · Cornerstone First Mortgage NMLS #173855 · Equal Housing Lender. Educational content, not a loan commitment and not legal or tax advice. Assessment levels, the state equalization factor, county tax rates and city rental ordinances change, and the figures here carry the date we verified them. Confirm current requirements with the county assessor, the county clerk, your CPA, or an Illinois real estate attorney before you buy. Loans are subject to buyer and property qualification.