If Illinois has over-valued your home, you overpay property tax every year until you fix it. Filing an appeal is a standard, homeowner-friendly process — here is exactly how it works in Illinois, including the deadline, the governing law, and the five steps to file.
The Illinois deadline
The appeal window in Illinois is typically Varies by township, and the filing deadline is Within 30 days of publication (varies by township/county). Miss it and you generally wait a full year, so check your assessment notice the moment it arrives. See the national deadline calendar for how this compares.
How Illinois values your home
Illinois taxes only 33% of your home's market value (its assessment ratio), so an assessment notice showing $100,000 implies a market value of $300,030. Convert the notice to an implied market value before deciding whether to appeal. Illinois assesses most property at 33.33% of fair market value (Cook County uses a 10% residential classification), so appeals target market value and uniformity. The process is authorized under 35 ILCS 200/16-55 (board of review); Cook County classification ordinance.
How to appeal your property taxes in Illinois
Step 1. Check your township's assessment publication date and current assessed value.
Step 2. File an appeal with the county assessor during your township's open appeal window.
Step 3. Submit comparable sales or lack-of-uniformity evidence with the appeal.
Step 4. If denied, appeal to the county Board of Review within 30 days of publication.
Step 5. Escalate to the Illinois Property Tax Appeal Board (PTAB) or circuit court.
Build your evidence
The strongest case is a tight set of comparable sales — 3 to 5 similar homes near you that sold for less than your assessed value — plus any property-record errors you can document. You can also make an unequal-assessment argument if comparable homes are assessed for less than yours.
Don't forget exemptions
An appeal lowers your value, but a homestead exemption cuts your taxable base directly — and the two stack. Confirm you're enrolled with your county before you file.
The shortcut
Checking comps and building the packet is where most homeowners give up. TaxAppealAgent does it for you: check your Illinois property for $4.99 (credited), and if you're over-assessed we assemble the comparable-sales evidence and a Illinois-specific appeal letter for a flat $29. You file it and keep 100% of the savings. See the full Illinois appeal guide.