Williamson County property tax appeal 2027: deadline, forms and how to file
To appeal a Williamson County assessment, file with the Williamson County Board of Review by mail or in person; in Illinois the deadline is 30 days after the township assessment list is published (Cook County uses township filing windows). Confirm the exact date on your notice or with the assessor; we add each county's 2027 date here when it is published.
Williamson publishes the assessment list county-wide (not by township): the 2025 assessed values were published in the newspaper April 9-15, 2026 (Swinford Publications notice), and the 2025 Board of Review hearings began April 9, 2026. The BOR page says the 2026 Board is accepting complaints and hearings will begin after the Assessor's books close, anticipated March 2027.
Data as of 20 Oct 2026 · Williamson County Board of Review (the three County Commissioners)Check your own assessment
Free. We compare the value on your notice with recent sales of similar homes nearby and tell you whether an appeal is worth filing. Have your assessment notice and tax bill handy.
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How to file in Williamson County
- Step 1
File the appeal
Use the method your notice lists, usually Form PTAB-1A, by the deadline on the notice.
- Step 2 · before the hearing
Prepare and submit your evidence
Overvaluation must be shown by a preponderance of the evidence; a uniformity (equity) claim needs clear and convincing evidence. The strongest evidence is a recent arm’s-length purchase of your home, or an appraisal as of January 1. Otherwise use at least three comparable sales, or for equity at least three similar nearby homes with their assessments and property record cards, in a grid. Bring a photo of your home and its property record card.
- Step 3
Meet, then hear
An informal review with Township assessor or Supervisor of Assessments comes first; if you decline the offer, the Williamson County Board of Review hears the case. Most reductions happen at the first step.
Before you file: how to read your notice · evidence that works · informal vs formal hearing · when not to appeal
Forms
| Form | Number | Use | Format |
|---|---|---|---|
| Residential Appeal (Property Tax Appeal Board) | PTAB-1A | Only after the Board of Review decides: the state appeal, due 30 days after the board’s written notice. Can also be filed online through PTAB eFile. | Fillable PDF |
Appeal levels
| Level | Who hears it | Deadline | Cost |
|---|---|---|---|
| Informal review | Township assessor or Supervisor of Assessments | Before the Board of Review deadline | Free |
| Board of Review | Williamson County Board of Review (the three County Commissioners) | 30 days after the assessment list is published | Free |
| Property Tax Appeal Board | Illinois Property Tax Appeal Board (state) | 30 days after the Board of Review’s written decision | No filing fee |
| Court | Circuit court (administrative review), or a tax objection in Williamson County circuit court | 35 days after the PTAB decision; tax objections follow the tax-bill penalty date | Court costs |
What evidence the board accepts
Overvaluation must be shown by a preponderance of the evidence; a uniformity (equity) claim needs clear and convincing evidence. The strongest evidence is a recent arm’s-length purchase of your home, or an appraisal as of January 1. Otherwise use at least three comparable sales, or for equity at least three similar nearby homes with their assessments and property record cards, in a grid. Bring a photo of your home and its property record card.
Williamson County questions
When is the Williamson County appeal deadline for 2027?
No 2027 date is published yet. The board’s rule: Complaints must be filed within 30 days after publication of the assessment list by the Supervisor of Assessments; complaints sent via USPS count as filed on the postmark date and other carriers on the shipper's tracking date; mail sent to the wrong address is invalid. Faxed or emailed complaints are not accepted (2025 rules).
How do I appeal my assessment in Williamson County?
File a written complaint on the board’s form with the Williamson County Board of Review (the three County Commissioners), Williamson County Board of Review, 407 N. Monroe Street, Suite 205, Marion, IL 62959. Mailed complaints count as filed on the postmark date.
Should I talk to the assessor first?
Yes. The township assessor or the Williamson County Supervisor of Assessments can fix record errors informally. Still file with the Williamson County Board of Review (the three County Commissioners) by the deadline: a board complaint is required before any state appeal.
What evidence works best?
A recent arm’s-length purchase of your home or an appraisal as of January 1. Otherwise, at least three comparable sales, or three similar nearby homes with lower assessments, with property record cards and photos.
How do I contact the Williamson County Supervisor of Assessments?
Mail: Williamson County Board of Review, 407 N. Monroe Street, Suite 205, Marion, IL 62959. Phone: 618-997-1301 ext. 5380. Hours and walk-in details: williamsoncountyil.gov.
What if the Board of Review says no?
Appeal to the Illinois Property Tax Appeal Board within 30 days of the board’s written decision. There is no fee, and you can file online through PTAB eFile. A lowered value on an owner-occupied home carries over for the rest of the assessment period.
Check whether yours is over-assessed
Nearby counties
Franklin County · Johnson County · Saline County · Union County · Jackson County · Pope County · Hamilton County
- Williamson County Board of Review
- Williamson County Supervisor of Assessments
- Williamson County Board of Review Rules and Procedures 2025 (PDF)
- Williamson County Assessment Changes 2025 publication (PDF)
- Illinois State Board of Elections County Officers directory
- 35 ILCS 200/16-55 — Board of Review complaints
- 35 ILCS 200/12-10 — Publication of assessments
- 35 ILCS 200/16-160 — Appeal to the Property Tax Appeal Board
- Illinois DOR — Assessment Appeals
- Property Tax Appeal Board — Filing your appeal
- Property Tax Appeal Board — FAQ
- U.S. Census Bureau, county population estimates (2024) and county gazetteer (2024).