Illinois Property Tax Protest Guide for 2026
Reviewed by RedTools Research Team, with Illinois assessment-appeal methodology review.
Last updated: April 30, 2026
Illinois has the second-highest effective property tax rate in the country (after New Jersey), and the appeal process is unusually multi-layered — especially in Cook County. Effective rates of 2.0% to 2.5% are common in Cook, DuPage, Lake, and Will counties. Multiple appeal venues mean you have several shots at a reduction over a 12–18 month window.
Illinois Filing Deadline
Outside Cook County, you generally have 30 days from the date of publication in the local newspaper of your township’s assessment changes. Cook County is different: it operates on a triennial reassessment cycle (every three years per township), and each township has its own appeal window staggered through the year. Always confirm with your specific Township Assessor or the Cook County Assessor’s public schedule.
Cook County’s Three Appeal Levels
Cook County is unique because you have three sequential opportunities to appeal in a given assessment year:
- Cook County Assessor’s Office (CCAO). First-level appeal during your township’s open window (assessor publishes the schedule). File online at cookcountyassessor.com.
- Cook County Board of Review (BOR). Independent of the assessor; opens after the assessor closes. Each township has its own BOR window. File online via the BOR portal.
- Illinois Property Tax Appeal Board (PTAB) or Cook County Circuit Court. Appeal of the BOR decision. PTAB is administrative (no fee); Circuit Court is a tax-objection complaint and requires the prior tax bill be paid in full.
Each of those levels is a fresh chance — not just a review of the previous decision. Many Cook homeowners win at the BOR after losing at the assessor.
Outside Cook County
Other Illinois counties (DuPage, Lake, Will, McHenry, Kane, Madison, St. Clair, etc.) typically use:
- Township Assessor — informal review.
- County Board of Review — formal appeal, typically 30 days after publication.
- Illinois PTAB — statewide administrative appeal of the Board of Review decision.
Statutory authority: 35 ILCS 200/16-55 (BOR), 35 ILCS 200/16-160 (PTAB).
What to Argue in Illinois
- Lack of uniformity. Illinois statute 35 ILCS 200/9-145 requires uniform assessment within a township. If similar properties are assessed at lower rates than yours, you have a uniformity argument that often wins even when sale comps are weak.
- Overvaluation. Recent comparable sales below your assessor’s estimated market value (your assessment ÷ the township equalization factor).
- Property record errors. Square footage, lot size, age, condition rating.
Illinois Multiplier (Equalization Factor)
Illinois uses a state equalization factor (the “multiplier”) on top of township-level assessment ratios. Cook County’s multiplier is typically around 2.7–3.0; downstate counties run closer to 1.0. Your assessed value × the multiplier = the equalized assessed value, which is multiplied by the local tax rate to compute your bill. To compute implied market value, you typically use: Equalized assessed value ÷ statutory assessment level (33-1/3% in most of Illinois) = implied market value. Comparable sales must support a value below that for a successful appeal.
Illinois Counties
| County | Major Cities |
|---|---|
| Cook | Chicago, Evanston, Schaumburg, Cicero |
| DuPage | Naperville, Wheaton, Downers Grove |
| Lake | Waukegan, Buffalo Grove, Vernon Hills |
| Will | Joliet, Bolingbrook, Plainfield |
| Kane | Aurora, Elgin, Geneva |
| McHenry | Crystal Lake, Algonquin, Woodstock |
| Madison | Edwardsville, Granite City, Alton |
| St. Clair | Belleville, East St. Louis, O’Fallon |
Common Illinois Mistakes
- Stopping at the assessor. Cook County homeowners should also file at the Board of Review — it’s a fresh chance.
- Forgetting uniformity. When sale comps are weak, lack-of-uniformity comps (similar properties assessed lower than yours) often carry the day.
- Missing the township window. Each Cook township opens and closes independently.
- Confusing the multiplier with the assessment level. Both reduce your assessed value to market value — understand them separately.
Illinois References
- Illinois Department of Revenue — Property Tax
- Illinois Property Tax Appeal Board (PTAB)
- Cook County Assessor
- Cook County Board of Review
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