In Cook County, several separate offices each control one piece of your property tax bill. The Assessor sets the value and grants exemptions. The Board of Review hears appeals. The Illinois Department of Revenue sets a statewide multiplier. The County Clerk calculates tax rates, and the Treasurer mails the bills. Because of this, a homeowner may have two chances to appeal in the same year, plus a state appeal after that, and an exemption that is missing from a bill can be fixed without a value appeal. This guide follows the cycle in order.

The short answer

  • Appeal to the Assessor first, then the Board of Review. Each township has its own window, usually about 30 days, and you can file with the Board even if you skipped the Assessor.
  • 2026 is the south and west suburbs’ reassessment year. Chicago is next, in 2027. You can appeal in any year, not just a reassessment year.
  • The state multiplier for tax year 2025 is 3.0300. It multiplies your assessed value, and any reduction you win, before exemptions come off.
  • Exemptions cut EAV directly. The homeowner exemption is $10,000 and the senior exemption is $8,000. A missing one can be fixed with a Certificate of Error.
  • The second installment carries every change. Its due date moves each year. The tax year 2025 bill was due October 1, 2026.

The triennial reassessment

Cook County is split into three regions for reassessment: the north suburbs, the west and south suburbs, and the City of Chicago. Each region is reassessed every three years, so one region is reassessed each year. That schedule comes from the Board of Review’s overview of the county property tax system (opens in a new tab). In 2026 the Assessor is reassessing the south and west suburbs, as its announcement of the 2026 reassessment (opens in a new tab) explains. Under the three-year rotation, the City of Chicago is next, in 2027, followed by the north suburbs. The county has 38 townships, and your township is shown on your tax bill and your assessment notice. You receive a notice when your property is reassessed. You can appeal every year when your township is open, not only in a reassessment year.

The Treasurer’s primer, How the Illinois Property Tax System Works (opens in a new tab), explains the assessment levels. Residential property, including apartment buildings, and vacant land are assessed at 10% of fair cash value. Commercial and industrial property is assessed at 25%. For a home, the assessed value on the notice should be about one-tenth of what the house would sell for. Check that the market value on the notice is close to a realistic sale price, and that the building facts (square footage, age, number of units, basement, garage) are correct.

Step one: appeal to the Assessor

The Cook County Assessor’s Office takes appeals by township. According to the Board of Review overview, each township is open for 30 days after its assessment notices are mailed, and results are posted about two months after the township closes. After all appeals in a township are finished, its assessments are certified and passed to the Board of Review.

A homeowner usually wins by showing that comparable homes are assessed lower, or that the property would sell for less than the Assessor’s estimate. A recent arm’s-length purchase price, an appraisal close to the valuation date, or proof of a factual error is direct evidence.

Step two: the Board of Review

The Board of Review is a three-member, quasi-judicial body that is independent of the Assessor. Its decision sets the final county value for the tax year. You can file with the Board even if you skipped the Assessor appeal. The Board groups the 38 townships into roughly eight filing groups, and each group stays open for at least 30 days. The 2026 session calendar (opens in a new tab) shows these dates:

  • Group 1 (Evanston, New Trier, Norwood Park, Oak Park, River Forest, Riverside, Rogers Park): filed August 3 to September 1, 2026; evidence due September 11.
  • Group 2 (Berwyn, Cicero, Elk Grove, Lakeview, Maine, Palos): August 31 to September 29, 2026; evidence due October 9.
  • Group 3 (Lyons, Northfield, Stickney, West Chicago): October 8 to November 6, 2026; evidence due November 16.

If your township isn’t listed yet, the Board says you can pre-register in its online portal. The residential appeals page (opens in a new tab) explains who may file. Individuals can represent themselves. Property owned by a corporation or LLC must be appealed by an attorney. A consultant may not represent a homeowner.

The Board’s FAQ (opens in a new tab) covers the practical details. Taxpayer hearings are held by phone, and you can waive the hearing without penalty because analysts review files the same way either way. Useful evidence includes a dated photo of your home’s exterior, photos and PINs of the comparable homes you cite, an appraisal, and affidavits or fire and flood reports. A signed statement explaining why you think you are over-assessed also helps. You can find comparables using CookViewer, the county’s GIS map. Evidence can be submitted up to five days before the hearing. After hearings, each township reopens for a short re-review period before the decisions become final.

Step three: PTAB or circuit court

If the Board of Review’s decision still seems wrong, you can go to the Illinois Property Tax Appeal Board (PTAB) or to circuit court. PTAB’s filing instructions (opens in a new tab) say you must file within 30 days of the Board of Review’s written decision. Homeowners use the Residential Appeal form, filed through PTAB’s eFiling system or by mail to Springfield. Fax and email are not accepted, and appellants with an attorney must e-file. Evidence should support the basis you checked on the form, such as at least three comparable sales, an appraisal, assessment data for comparable properties, or closing documents from a recent purchase. The Treasurer’s primer warns that PTAB cases can take years and that you generally must keep paying the bills based on the contested value while the case is pending. The Treasurer’s Office issues property tax refunds.

The equalization factor (the “multiplier”)

Illinois law sets assessments at 33⅓% of fair cash value. Cook County assesses homes at 10%, so the Department of Revenue applies an equalization factor to bring the county’s overall level up to the state standard. The Treasurer’s primer says Cook’s factor has been at least 2, and sometimes above 3, in recent decades. The sample bill in the primer uses 3.0163 for tax year 2023. The latest final factor is 3.0300 for tax year 2025, announced by the Department of Revenue on June 18, 2026 (opens in a new tab). The factor applies to every property in the county the same way. You can’t appeal it as a homeowner, but it multiplies any reduction you win at the Assessor or Board of Review.

The Clerk calculates the bill in this order: assessed value × equalization factor, minus exemptions, equals the adjusted equalized assessed value (EAV). The adjusted EAV is then multiplied by the combined tax rate of all your taxing districts.

Exemptions that lower EAV

Exemptions reduce EAV directly. The main ones for homeowners:

  • Homeowner exemption: $10,000 off EAV, in effect since tax year 2017. The Treasurer’s homeowner exemption page (opens in a new tab) lists eligible primary residences as single-family homes, townhouses, condominiums, co-ops, and apartment buildings of up to six units. It renews automatically unless the property was sold in the last year.
  • Senior exemption: $8,000 off EAV for an owner-occupant who is 65 or older during the tax year. It can be combined with the homeowner exemption.
  • Senior Freeze: keeps EAV at the base-year level while you remain eligible. Your bill can still rise if tax rates go up or you add improvements. The Department of Revenue’s exemption summary (opens in a new tab) requires age 65 and total household income of $75,000 or less for tax year 2026 (payable 2027), $77,000 for 2027, and $79,000 for 2028 and later. Some county pages, including the Treasurer’s Senior Freeze page (opens in a new tab), still show the older $65,000 limit. You must reapply every year.

The Treasurer’s primer also describes a Cook-only Long-time Occupant exemption for households with income of $100,000 or less that have lived in the home for 10 years (5 with purchase assistance), and a $2,000 EAV exemption for persons with disabilities. You apply for exemptions through the Assessor. They first show up on the second-installment bill. If one is missing, the Board of Review overview says you can ask the Assessor for a Certificate of Error after second-installment bills are mailed. If you already paid, the Treasurer issues the refund. For how these compare with programs in other states, see our senior relief guide.

Two installments, and why the second one differs

By law, the first installment is 55% of the prior year’s total tax and is typically due March 1. It does not reflect this year’s assessment, appeals, exemptions, or rates. The second installment is the full year’s tax minus what the first installment billed. The Board of Review explains that the second installment cannot be calculated until it has finished appeals in all 38 townships, so its due date varies from year to year. Recent second installments have come late. The tax year 2025 second-installment bills were mailed around September 1, 2026, and were due October 1, 2026, about two months later than usual, according to a Cook County announcement (opens in a new tab). The county blamed delays from an overhaul of the property tax technology system. Check the due date printed on your bill or at the Treasurer’s website (opens in a new tab). Any change shows up in the second bill: a reassessment, an appeal result, a new equalizer, new levies, or an exemption added or dropped. Late payments accrue interest of 0.75% per month. See our guide to reading a property tax bill for a line-by-line walkthrough.

Hypothetical worked example

Every number below is invented for illustration, including the multiplier and tax rate. These are not current values. A house has a market value of $300,000, so its assessed value at 10% is $30,000. With a multiplier of 3.0, the EAV is $90,000. Subtracting the $10,000 homeowner exemption gives $80,000. At a combined rate of 7%, the year’s tax is $5,600. Last year’s total was $5,000, so the first installment was $2,750 (55%), and the second installment is $2,850. If the owner had won a 10% reduction in assessed value to $27,000, the EAV after the exemption would be $71,000 and the tax $4,970, which is $630 less, all of it coming off the second installment. If the owner also qualified for the senior exemption, another $8,000 of EAV would come off.

Common mistakes

  • Waiting for the tax bill to appeal. The township windows run on their own schedule and close after about 30 days.
  • Withholding payment while an appeal is pending. Pay both installments on time.
  • Not reapplying for the Senior Freeze each year.
  • Using comparables without PINs or photos, or homes that differ a lot in size or age.

If you also want to see how exemptions work in other states, our homestead exemption guide covers the basics. For office contacts, see our Cook County page or the Illinois county directory, and use our appeal preparation checklist to put your evidence together.

Frequently asked questions

When can I appeal my Cook County property taxes?

When your township is open. The Assessor opens each township for about 30 days after notices are mailed. The Board of Review then opens its own township groups, each for at least 30 days. Check both offices’ calendars for your township.

Is Chicago being reassessed in 2026?

No. The 2026 reassessment covers the south and west suburbs. Chicago is next in the rotation, in 2027. Chicago owners can still appeal their 2026 values.

What is the Cook County multiplier for 2025?

The final tax year 2025 equalization factor is 3.0300. The Department of Revenue sets it, and homeowners cannot appeal it.

When is the Cook County second installment due?

It changes each year. The tax year 2025 second installment was due October 1, 2026. The first installment is usually due March 1. Your bill shows the exact date.

What if my homeowner or senior exemption is missing from my bill?

Ask the Assessor for a Certificate of Error after second-installment bills are mailed. If you already paid, the Treasurer issues the refund. Our homestead exemption guide explains how these exemptions work in general.

Sources reviewed October 13, 2026; reassessment year, multiplier, and second-installment dates updated October 26, 2026. The Assessor’s own website could not be reached for this review, so check township dates and exemption deadlines with the Assessor’s Office directly.