How Cook County Property Assessments Work

The triennial reassessment cycle

Cook County is divided into three geographic groups, and each group is reassessed once every three years on a rotating schedule:

• ·City of Chicago — reassessed every third year
• ·North and Northwest suburbs — reassessed the year before Chicago
• ·South and West suburbs — reassessed the year before that

This means your property might go two years without any change, then jump significantly in the reassessment year — especially if real estate prices moved during those two years.

How the CCAO calculates your assessed value

The Cook County Assessor's Office (CCAO) uses mass appraisal techniques — statistical models that estimate property values across large areas using factors like:

• ·Recent arm's-length sales in the neighborhood
• ·Building size, age, and property class
• ·Land characteristics and location factors
• ·CCAO neighborhood codes (not the same as ZIP codes or city neighborhoods)

The result is an estimated market value. For residential properties (Class 2), the assessed value is set at 10% of that estimated market value.

The state equalization factor

Illinois law requires that all counties assess property at a statewide equalized rate of 33.33%of market value. Since Cook County uses 10%, the Illinois Department of Revenue applies a multiplier — the state equalization factor (sometimes called the “state multiplier”) — to bring Cook County assessments up to the statewide target.

In recent years this multiplier has been around 3.0x, so:

Your EAV (minus any exemptions) is the number your tax rate is applied to.

Exemptions that reduce your bill

Before your tax rate is applied, certain exemptions reduce your EAV. The most common for homeowners:

• ·Homeowner Exemption — $10,000 reduction in EAV for primary residence (~$300/yr savings)
• ·Senior Exemption — additional $8,000 EAV reduction for homeowners 65+
• ·Senior Freeze — freezes EAV for qualifying seniors with income limits

Exemptions are applied before your tax bill is calculated. If you're not claiming every exemption you qualify for, you're leaving money on the table — separate from any appeal.

The appeal process

After reassessment, you have a window — typically 30 days from the mailing of your assessment notice — to file an appeal first with the CCAO, and then (if needed) with the Cook County Board of Review. Missing this window means waiting until the next reassessment year.

There are two main appeal arguments:

• ·Overvaluation — your home's market value is lower than the CCAO thinks (requires an appraisal or recent sale)
• ·Uniformity — similar properties nearby are assessed lower per square foot than yours (no appraisal needed)