Cook County’s property tax reassessment schedule runs on a three-year rotation, and in 2026 the south and west suburban townships are the district under review. Properties in the north suburbs and the City of Chicago keep their existing assessed values this year unless a permit, subdivision, or other special change triggers a fresh look. Knowing where your property sits in the cycle tells you when to expect a new valuation, when your appeal window opens, and why your tax bill can jump one year and hold steady for the next two.
How the Three-Year Rotation Works
The Cook County Assessor’s Office divides the county into three reassessment districts: the north suburbs, the south and west suburbs, and the City of Chicago.1Cook County Assessor’s Office. About the Cook County Assessor’s Office Each year, one district goes through a full property-by-property revaluation while the other two sit idle. The Assessor cycles through the three groups in order, so every property in the county gets a fresh look at its market value once every three years.2Cook County Assessor’s Office. Assessment and Appeal Calendar
During off-cycle years, your assessed value stays the same unless something specific triggers a change: new construction, a building permit, or a parcel split. The predictability helps with budgeting. It also means your assessed value can lag the market, so when your reassessment year arrives, the new number may reflect two or three years of accumulated price changes at once.
Which Townships Are Reassessed in 2026
The south and west suburbs are the active district for 2026. The townships scheduled for new valuations are:
- Oak Park, River Forest, Riverside, Berwyn, Cicero, Stickney, Lyons, and Proviso
- Palos, Lemont, Worth, Orland, Bremen, Calumet, Thornton, Rich, and Bloom
Property owners in these townships will receive a reassessment notice by mail once their township opens for review. The Assessor’s website publishes exact mailing dates and appeal deadlines for each township as they become available.2Cook County Assessor’s Office. Assessment and Appeal Calendar Not every township opens on the same day. The Assessor releases them in sequence over the course of the year, so two neighbors in different townships may see notices weeks or months apart.
What About the North Suburbs and Chicago
If your property is in the north suburbs or the City of Chicago, you will not receive a new valuation in 2026 absent special circumstances. The north suburbs completed their cycle in 2025, covering townships including Barrington, Evanston, Schaumburg, Palatine, and Niles.3Cook County Assessor’s Office. Learn About Reassessments Chicago sits in its own third of the rotation and takes its turn on a different year in the cycle.
Even in an off year, your tax bill can still change. The state equalization factor, local tax rates, and any adjustments to your exemptions all move independently of the reassessment schedule, and each one can push your bill up or down while your assessed value stays flat.
The Reassessment Notice and Your Appeal Window
When your township opens, an official notice arrives in the mail. It shows your property’s address, its physical characteristics, and its updated estimated fair market value alongside the previous values so you can see how much the estimate changed.2Cook County Assessor’s Office. Assessment and Appeal Calendar Land value and building value are broken out separately, and errors in either component are grounds for an appeal.
The notice prints your 14-digit Property Index Number (PIN), which you’ll need for any appeal filing.4Cook County Assessor’s Office. Where Do I Find My PIN It also lists the date your township opens for appeals and the last date to file, typically 30 days after the notice is mailed.5Cook County Assessor’s Office. Overview of How Appeals Work Miss that window in your reassessment year and the higher number stays in place until the township reopens, which for this cycle means waiting three years.
How a New Valuation Turns Into a Tax Bill
The Assessor’s market value estimate isn’t the number used to calculate your taxes. Cook County applies a classification system that converts market value into a lower assessed value based on property type. Residential properties are assessed at 10 percent of estimated market value, while commercial and industrial properties are assessed at 25 percent.6Cook County Assessor’s Office. Definitions for the Classification of Real Property A home the Assessor values at $300,000 carries an assessed value of $30,000. These percentages sit in the Cook County Real Property Assessment Classification Ordinance, which the County Board is authorized to adopt under state law.7Cook County Government. How Assessments Work in Cook County
Then comes the state equalization factor. Illinois law requires all counties to assess property at one-third (33.33 percent) of market value, but Cook County assesses residential property at 10 percent. To bridge that gap, the Illinois Department of Revenue applies a multiplier to every assessed value in the county. For the 2025 tax year, the tentative equalization factor is 2.8683, calculated by dividing Cook County’s three-year weighted average assessment level of 11.62 percent into 33.33 percent.8Illinois.gov. 2025 Cook County Tentative Multiplier Announced Multiplying your assessed value by the factor produces your equalized assessed value, or EAV. A $30,000 assessed value multiplied by 2.8683 comes out to an EAV of roughly $86,049. The factor changes every year, so your EAV can shift even in years when the Assessor doesn’t touch your value.
Exemptions come off the EAV before the tax rate is applied. The Homeowner Exemption, available to anyone who owns and occupies their primary residence, reduces EAV by $10,000 and saves the average Cook County homeowner roughly $950 per year; once granted, it typically renews automatically.9Cook County Treasurer’s Office. Homeowner Exemption10Cook County Assessor’s Office. Property Tax Exemptions Homeowners 65 or older can add a Senior Citizen Homestead Exemption worth up to $8,000 in EAV reduction.11Illinois Department of Revenue. Property Tax – Exemption Information (PIO-74) The Senior Citizen Assessment Freeze locks in EAV at the level it was when the senior first qualified, with an income limit of $65,000 that rises to $75,000 for Tax Year 2026.12Cook County Assessor’s Office. Assessor Kaegi Praises Passage of Property Tax Relief for Senior Homeowners Veterans with a service-connected disability can claim an exemption whose size depends on the disability level; unlike the others, it requires annual filing.
Cook County sends two tax bills per year. The first installment is 55 percent of the prior year’s total tax; for Tax Year 2025 it was due April 1, 2026. The second installment reflects the actual tax owed after the Assessor’s values, equalization factor, exemptions, and local tax rates are all finalized, which is why it’s usually a different amount than the first. Late payments carry a penalty of 0.75 percent per month on the unpaid balance and cannot be waived.13Cook County Property Tax Portal. Pappas Says Pay Property Tax Bills Online Now at cookcountytreasurer.com
If Your New Value Looks Wrong
The Assessor’s Office is the first place to challenge a reassessment. You generally have 30 days from the mailing date of your notice to file, with the exact deadline printed on the notice itself.14Cook County Assessor’s Office. Residential Appeals Two grounds carry most residential appeals. Lack of uniformity means pointing to comparable properties in your neighborhood, similar in square footage, age, building type, and classification code, that carry lower assessed values relative to their market values. Overvaluation means arguing the Assessor’s estimate exceeds what your property would actually sell for, supported by evidence like a recent appraisal, a closing statement, or photographs of conditions that reduce value. Filing is available online, and the portal lets you upload documents and save drafts before the deadline.15Cook County Assessor. File an Appeal Online
If the Assessor’s decision doesn’t resolve the dispute, the Cook County Board of Review is a separate elected body that opens its own appeal period for each township on a schedule it publishes independently.16Cook County Board of Review. Cook County Board of Review You do not have to file with the Assessor first to appeal to the Board. Its determination, not the Assessor’s original number, becomes the final local word on your assessment.
Beyond that, the state-level Property Tax Appeal Board (PTAB) accepts petitions within 30 days of the postmark on the Board of Review’s written decision.17Property Tax Appeal Board. Frequently Asked Questions Filing is free, but appeals must be mailed or hand-delivered rather than faxed, and PTAB warns that USPS postmarks don’t always match the date the post office first accepted the envelope, so certified mail or a requested manual postmark is the safest proof of timely filing. PTAB cases can take over a year to resolve, and the Board can reduce your assessment back to the tax year in question.