Property taxes in Illinois are calculated by taking a fraction of your home’s fair market value, multiplying it by a county equalization factor to get your Equalized Assessed Value (EAV), subtracting any exemptions you qualify for, and then applying the combined tax rate of every local district that serves your address. The fraction is 33⅓ percent of market value in most of the state and 10 percent for residential property in Cook County. Because the final bill runs through four separate steps, a change at any one of them can move your tax noticeably from one year to the next.
Step 1: Your Assessed Value
Every bill starts with a local assessor estimating what your property would sell for on the open market. Assessors look at square footage, age, condition, and lot size, then compare your property to recent sales of similar homes nearby. This is called mass appraisal because thousands of properties are valued at once rather than inspected individually.1Cook County Assessor’s Office. How Properties Are Valued
Illinois does not reassess every property every year. Under 35 ILCS 200/9-215, counties with fewer than 3,000,000 residents follow a four-year reassessment cycle. Cook County reassesses on a three-year rotation, splitting the county into the City of Chicago, the north suburbs, and the south suburbs, with one area revalued each year.1Cook County Assessor’s Office. How Properties Are Valued Between reassessment years, your assessed value generally stays the same unless you make major improvements or the assessor corrects an error.
Illinois does not tax the full market value. Under 35 ILCS 200/9-145, most property is assessed at exactly 33⅓ percent of fair market value. A $300,000 home starts with an assessed value of $100,000.2Justia. Illinois Code 35 ILCS 200 – Property Tax Code – Division 4 Valuation Procedures
Cook County is the exception. Because it classifies property by use, residential homes there are assessed at 10 percent of fair market value rather than 33⅓ percent.3Illinois Department of Revenue. PIO-16, An Overview of Property Tax That lower starting ratio does not translate into lower taxes on its own; the equalization factor and local rates make up the difference. It just means the arithmetic looks different depending on which side of the county line your home sits.
Step 2: The Equalization Factor and Your EAV
To keep the burden consistent across all 102 counties, the Illinois Department of Revenue publishes an annual multiplier for each county called the state equalization factor. The department compares actual sale prices to assessed values over a three-year period. If a county’s median assessment level is above or below the required 33⅓ percent, the equalization factor pulls it back in line.4Illinois Department of Revenue. 2024 Cook County Final Multiplier Announced
Multiplying your assessed value by the equalization factor produces your Equalized Assessed Value, or EAV. This is the number that actually drives your tax bill. A county where assessors have been undervaluing properties will get a multiplier above 1.0, pushing EAVs up. A county assessing right at the mark will see a factor close to 1.0.
Step 3: Exemptions That Reduce Your Taxable EAV
Before any tax rate is applied, Illinois subtracts exemptions from your EAV. These are not credits against your bill. They lower the taxable value itself, so the dollar savings depend on your local tax rate. The common exemptions apply only to your principal residence, so investment properties and second homes are not eligible.
General Homestead Exemption
If you own and occupy your home as your principal residence, you can claim the General Homestead Exemption under 35 ILCS 200/15-175. The maximum EAV reduction is $10,000 in Cook County, $8,000 in counties bordering Cook County, and $6,000 elsewhere in the state.5FindLaw. Illinois Code Chapter 35 Revenue 200/15-175 General Homestead Exemption In a district with an 8 percent composite tax rate, a $10,000 EAV reduction knocks $800 off the annual bill.
Senior Citizens Homestead Exemption
Homeowners who turn 65 by December 31 of the assessment year get an additional reduction. The maximum is $8,000 in Cook County and the contiguous counties and $5,000 in the rest of the state. It stacks on top of the General Homestead Exemption.6Illinois Department of Revenue. Property Tax Relief – Homestead Exemptions, PTELL, and Senior Citizens Real Estate Tax Deferral Program
Senior Citizens Assessment Freeze
The Senior Freeze is a separate benefit from the Senior Homestead Exemption and often more valuable. If you are 65 or older and your total household income is $65,000 or less, the freeze locks your EAV at the level in the year before you first applied. Market value can keep climbing, but the taxable EAV stays frozen; the exemption equals the difference between the current EAV and your frozen base year.6Illinois Department of Revenue. Property Tax Relief – Homestead Exemptions, PTELL, and Senior Citizens Real Estate Tax Deferral Program You have to reapply every year and meet the income cap each year to keep it.
Disabled Veterans and Disabled Persons
Veterans with a service-connected disability receive an EAV reduction that scales with the disability rating: $2,500 for 30–49 percent, $5,000 for 50–69 percent, and $250,000 for 70 percent or higher. The top tier effectively eliminates property tax for most qualifying veterans.7Cook County Assessor’s Office. Veterans with Disabilities Exemption A separate Disabled Persons’ Homestead Exemption provides a smaller annual reduction for non-veteran homeowners with disabilities. Both require documentation and periodic renewal.
Step 4: The Composite Local Tax Rate
Your tax rate is not set by any single government body. Every local taxing district that covers your address, including school districts, the municipality, the county, park districts, library districts, fire protection districts, and community colleges, submits its own annual levy to the county clerk. The levy is the dollar amount that district needs to collect. By law, those levies must be filed by the last Tuesday in December.8Illinois General Assembly. 35 ILCS 200 Property Tax Code – Section 18-15
The county clerk divides each district’s levy by the total EAV of all property within that district’s boundaries. The result is the tax rate for that district, expressed as a percentage or as dollars per $100 of EAV.9Illinois General Assembly. Illinois Code 35 ILCS 200 Article 18-45 – Computation of Rates Your composite rate is the sum of every overlapping district’s individual rate. A typical Illinois homeowner sits within 10 to 15 taxing districts, and school districts usually take the largest share.
What PTELL Does and Doesn’t Cap
The Property Tax Extension Limitation Law limits how fast most taxing districts can grow their levies year over year. For non-home-rule districts, the annual increase in the total tax extension is capped at the lesser of 5 percent or the prior year’s increase in the Consumer Price Index. Districts can exceed the cap only for new construction or through a voter-approved referendum.10Illinois Department of Revenue. What Is the Property Tax Extension Limitation Law (PTELL)?
PTELL does not cap your individual bill. If your EAV rises faster than average, because of a renovation or a hot local market, your share of the district’s levy grows even when the total levy stays within the cap.
Putting the Pieces Together
Once you have the four inputs, the formula is simple:
(EAV − Exemptions) × Composite Tax Rate = Annual Property Tax
Here is how it works for a $300,000 home outside Cook County with a composite rate of 8 percent and a homeowner claiming the General Homestead Exemption:
- Fair market value: $300,000
- Assessed value at 33⅓%: $100,000
- Equalization factor of 1.0: EAV = $100,000
- General Homestead Exemption: −$6,000
- Net taxable EAV: $94,000
- Composite tax rate: 8.0%
- Annual tax bill: $7,520
The same $300,000 home in Cook County would start at a 10 percent assessment ratio, producing an assessed value of $30,000. After the equalization factor (often well above 1.0 in Cook County) and a $10,000 Homestead Exemption, the net EAV and final bill come out quite differently. Comparing raw tax rates between Cook County and downstate is misleading without accounting for the assessment ratio underneath. The revenue is then split proportionally among the school districts, municipalities, and other local bodies that levied against your property.11Illinois Department of Revenue. What Is Property Tax and How Is It Collected and Distributed?
When the Bill Arrives
Illinois property taxes are paid in arrears. The bills you get in 2026 cover the 2025 tax year. The one-year lag dates back to the Great Depression, when officials delayed collection to help struggling homeowners.12Cook County Treasurer. Why We Pay Property Taxes in Arrears If you are buying a home, the seller owes for the portion of the tax year before closing and will typically give you a credit at settlement.
Most counties outside Cook split the bill into two installments due around June 1 and September 1. Cook County uses accelerated billing: the first installment, set at 55 percent of the prior year’s total, is mailed by January 31 and due March 1, with the second installment covering the balance usually due around August 1.13Illinois Department of Revenue. What Should I Do If I Have Not Received My Property Tax Bill? Missing a due date triggers a 1.5 percent monthly interest charge on the unpaid amount.
If the Number Looks Wrong
Because the assessor’s value is the first input in the whole calculation, a mistake there compounds through every step that follows. Pull your property record card from the assessor’s office and check the basics: square footage, number of bathrooms, lot size, condition rating. Clerical errors are more common than homeowners expect, and a phone call can fix one without a formal appeal.
If an informal correction doesn’t resolve it, file a written complaint on Form PTAX-230 with your county’s Board of Review, with evidence that the assessment is wrong: recent comparable sales, an independent appraisal, or photographs of the property’s condition.14Illinois Department of Revenue. Assessment Appeals – Property Tax Deadlines vary by county, so contact the Board of Review as soon as your assessment notice arrives. If the board rules against you, you have 30 days to appeal to the Illinois Property Tax Appeal Board.15Illinois Property Tax Appeal Board. Filing Your Appeal