How Cook County property tax is calculated
Your bill is the Equalized Assessed Value (EAV) minus exemptions, times the composite tax rate of every district where your property sits. The Assessor sets the market value, residential property is assessed at 10% of it, and the Illinois Department of Revenue's equalization factor (the "multiplier") turns that into EAV.[1][2]
Tax = (Market value × 10% × 3.03 − exemptions in EAV) × local tax rate
The Cook County Treasurer publishes a worked example. A $303,850 home in Niles, at the tax year 2023 factor of 3.0163 and a local rate of 8.532%, had an EAV of $91,650 and $7,819.58 in tax before exemptions. The Homeowner Exemption took off $853.20 and the Senior Exemption $682.56, for a total of $6,283.82.[4] Our calculator reproduces that bill to the cent. With the 2025 factor instead, the same home and rate would owe $6,319.40 with both exemptions, or $7,001.96 with the Homeowner Exemption only.
| Line | Amount |
|---|---|
| Property (market) value | $303,850 |
| × 10% assessment level = assessed value | $30,385 |
| × 3.0163 state equalizer = EAV | $91,650 |
| × 8.532% local tax rate = tax before exemptions | $7,819.58 |
| Homeowner Exemption ($10,000 × 8.532%) | −$853.20 |
| Senior Exemption ($8,000 × 8.532%) | −$682.56 |
| Total tax | $6,283.82 |
| First installment (estimated) | $3,473.03 |
| Second installment (final) | $2,810.79 |
Cook County property tax due dates
Cook County bills in two installments, one year in arrears: tax year 2025 was due April 1, 2026 (first installment) and October 1, 2026 (second installment).[5] The first installment is an estimate based on the prior year's bill; the second is the final bill with the new assessment, equalization factor, exemptions and rates.[1]
- April 1, 2026 — Tax year 2025 first installment
- October 1, 2026 — Tax year 2025 second installment
- March 4, 2025 — Tax year 2024 first installment
- December 15, 2025 — Tax year 2024 second installment
- December 15, 2026 — Annual tax sale (delinquent tax year 2023 taxes)
Unpaid taxes go to the annual tax sale; the next one, for delinquent tax year 2023 taxes, is scheduled for December 15, 2026.[6] Due dates for other large counties are on property tax due dates.
Cook County homeowner exemption and other exemptions
An exemption lowers your EAV, so it saves the exemption amount times your tax rate: at an 8.532% rate the $10,000 Homeowner Exemption is worth $853.20 a year.[7] Exemptions show up on the second-installment bill.
| Exemption | Reduction | Who qualifies |
|---|---|---|
| Homeowner | $10,000 off EAV | Owner-occupied principal residence on January 1 |
| Senior Citizen Homestead | $8,000 off EAV | Owner-occupant 65 or older during the tax year |
| Senior Citizen Assessment Freeze | EAV frozen at the base year | Age 65+, household income $65,000 or less |
| Veterans with Disabilities 30–49% | $2,500 off EAV | Service-connected disability rating, filed yearly |
| Veterans with Disabilities 50–69% | $5,000 off EAV | Service-connected disability rating, filed yearly |
| Veterans with Disabilities 70%+ | 100% exempt | Rating of 70% or more |
The Senior Freeze keeps your EAV from rising while you qualify, but the bill can still rise when tax rates go up.[8][9][10] The calculator does not model the freeze because it depends on your base-year EAV; use the EAV printed on your bill for the frozen year. More senior programs across counties are compared on property tax exemptions for seniors.
Cook County equalization factor
The final 2025 equalization factor for Cook County is 3.03, set by the Illinois Department of Revenue on June 18, 2026, down slightly from 3.0355 for 2024.[2] The factor evens out assessment levels between Illinois counties; it does not raise total taxes by itself, because the Clerk sets rates so each district's levy is collected.[1][4]
| Tax year | Factor |
|---|---|
| 2025 | 3.03 |
| 2024 | 3.0355 |
| 2023 | 3.0163 |
How much is the typical Cook County bill?
For tax year 2025 (billed in 2026) the median homeowner bill was $4,597 in the City of Chicago (+3.2%), $8,007 in the north and northwest suburbs (+6.7%) and $6,468 in the south and southwest suburbs (+3.4%).[3] Census data put the county-wide median at $6,349 in property tax on a $335,800 median home in 2024, an effective rate of about 1.89%.[11][12]
- City of Chicago$4,597
- North and northwest suburbs$8,007
- South and southwest suburbs$6,468
Total property taxes billed county-wide for tax year 2025 were $19.9 billion; taxes rose 3.9% while inflation was 3.1%.[3] Illinois as a whole is compared with other states on property tax rates by state.
Reassessment and how to appeal
Cook County reassesses one third of the county each year: the City of Chicago in 2024, the north and northwest suburbs in 2025 and the south and southwest suburbs in 2026.[3] You have 30 days after your reassessment notice to appeal to the Assessor; after that you can go to the Board of Review, then to the state Property Tax Appeal Board or Circuit Court.[4]
- Check the property characteristics on your notice (square footage, class, units).
- Compare your market value with similar homes nearby; most winning appeals show the home is valued higher than comparable properties.
- File with the Assessor within the township's window, then with the Board of Review if needed.
Common mistakes
- Multiplying the market value by the rate. The rate applies to EAV (about 30% of market value at the 2025 factor), not to the market value.
- Judging the year by the first installment. The first installment is 55% of last year's total (on the Treasurer's sample bill, $6,314.60 × 55% = $3,473.03), so a new assessment only shows up on the second.[4]
- Missing an exemption after buying. Exemptions renew automatically for long-time owners, but new owners must apply to the Assessor.[7]
- Using a neighbor's rate. Two homes a block apart can sit in different tax codes with different rates.
Other large counties work differently: Texas counties use 100% of market value with a Harris County property tax rate stack of many units, and California caps assessed value under Prop 13 (see Los Angeles County property tax). To compare any county, start from the property tax calculator.
Value too high? Try the free property tax assessment appeal calculator before the Cook County Board of Review deadline (not legal advice).
Frequently asked questions
How is Cook County property tax calculated?
Market value × 10% assessment level × the state equalization factor (3.03 for 2025) gives the Equalized Assessed Value. Subtract exemptions (such as $10,000 for the Homeowner Exemption) and multiply by your composite local tax rate.
When are Cook County property taxes due in 2026?
Tax year 2025 bills were due April 1, 2026 (first installment) and October 1, 2026 (second installment), according to the Cook County Treasurer.
How much does the Cook County homeowner exemption save?
It removes $10,000 of EAV, so it saves $10,000 times your tax rate: about $853 a year at an 8.532% rate.
What is the Cook County equalization factor for 2025?
3.03, the final factor announced by the Illinois Department of Revenue in June 2026 (3.0355 for 2024).
How long do I have to appeal my Cook County assessment?
30 days after the reassessment notice to appeal to the Assessor; after that the Board of Review hears appeals township by township.
Sources
- Understanding your Tax Year 2025 Second Installment tax bill
- Final 2025 Cook County equalization factor (3.0300)
- Tax Year 2025 Tax Bill Analysis
- How the Illinois Property Tax System Works (October 2025 update)
- Important Dates: property tax due dates
- Cook County Treasurer's Office home page (tax sale date)
- Homeowner Exemption
- Senior Citizen Homestead Exemption
- Senior Citizen Assessment Freeze Exemption
- Disabled Veteran Homestead Exemption
- Table B25103: Mortgage Status by Median Real Estate Taxes Paid (American Community Survey 2024 1-year)
- Table B25077: Median Value (Dollars), owner-occupied housing units (American Community Survey 2024 1-year)