How to Appeal Your Property Tax in Illinois

Illinois homeowners can appeal their property tax assessment if they believe it's too high. This guide covers the 2026 appeal deadline, required evidence, and step-by-step process.

How Illinois Assesses Property

33.33%of market value

Illinois assesses residential property at 33.33% of market value. This means if your home is worth $239,000, your assessed value would be $79,659.

Illinois assesses residential property at 33.33% of fair market value statewide. Cook County uses a 10% ratio for residential under its classification system.

The Appeal Process

Appeals are heard by the Board of Review. An informal review is available before filing a formal appeal.

County Assessor (Informal)

Board of Review

Property Tax Appeal Board (PTAB)

Circuit Court

Illinois Appeal Deadline

30 days from publication

Typical window: Year-round by township

See all 50 state deadlines for 2026 →

What Overassessment Costs Illinois Homeowners

The median home in Illinois is worth $239,000. If your assessment is just 10% too high, you may be overpaying:

~$495/year

Effective tax rate: 2.07% · Median value: $239,000

Check Your Illinois Assessment

Enter your address to see your estimated overassessment and Illinois filing deadline.

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Illinois Counties

Cook County

Median: $335,800 · Rate: 1.89%

Deadline: 30 days after receiving your reassessment notice

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DuPage County

Median: $409,100 · Rate: 1.91%

Deadline: 30 days after publication of township assessment roll

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Kane County

Median: $312,600 · Rate: 2.60%

Deadline: 30 calendar days after date of publication of the current year assessment list

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Lake County

Median: $287,300 · Rate: 2.94%

Deadline: 30-day deadline from the date of publication

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McHenry County

Median: $328,900 · Rate: 2.18%

Deadline: 30 days after the publication of your assessment

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Will County

Median: $240,500 · Rate: 2.05%

Deadline: 30 calendar days from the date of notice

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Key Terms for Illinois Homeowners

Assessment Ratio

The percentage of a property's market value that a state uses to calculate the assessed value for property tax purposes.

Informal Review

An optional first step in the appeal process where a property owner discusses their assessment directly with the assessor's office before filing a formal appeal.

Guides & Resources

Property Tax Appeal Resources

Best Appeal Services Compared

7 companies compared — pricing, coverage, and pros/cons for 2026.

2026 Appeal Deadlines

Every state's deadline, filing method, and what happens if you miss it.

Assessment Ratios by State

Every state's assessment percentage — from 4% to 100% — with worked examples.

9 Ways to Lower Your Property Taxes

From homestead exemptions to formal appeals — every method that works.

Savings Calculator

Check if you're overassessed — enter your assessed value to see potential savings.

Frequently Asked Questions

How do I appeal my property tax in Illinois?

In Illinois, you file a appeal with the Board of Review. An informal review is available before filing a formal appeal. The process has 4 levels: County Assessor (Informal), Board of Review, Property Tax Appeal Board (PTAB), Circuit Court.

When can I appeal my property tax in Illinois?

30 days from publication The typical window is Year-round by township.

What is Illinois's property tax assessment ratio?

Illinois assesses residential property at 33.33% of market value. Illinois assesses residential property at 33.33% of fair market value statewide. Cook County uses a 10% ratio for residential under its classification system.

How much can I save by appealing in Illinois?

The median home in Illinois is worth $239,000. If your assessment is 10% too high, you may be overpaying approximately $495 per year.