Cook County property tax appeal evidence checklist.

Start with the reason for appeal

Cook County residential appeal guidance identifies common reasons as uniformity, overvaluation, and incorrect property characteristics. Pick the strongest provable reason first, then build the packet around that reason.

Do not lead with the tax bill alone. The Assessor explains that an appeal is intended to correct the assessment and that the Assessor does not set property tax levies, rates, or bills.

Overvaluation evidence

For overvaluation, the file should answer a market-value question: what would the property likely sell for as of the relevant assessment date? Useful support can include a recent arm's-length purchase, closing statement, deed or transfer declaration, appraisal, and comparable sales.

Tie the evidence to a requested market value and assessed value. A bill increase, mortgage payment, or general affordability concern does not prove that the estimated market value is wrong.

Uniformity evidence

Uniformity evidence compares your assessment with comparable properties. The Assessor's comparable-property guidance says good comps should be similar by township and neighborhood, property class code, age, building square footage, land square footage, and other relevant characteristics.

CookViewer can help find filtered comparable properties, but the final packet should still explain why each comp is similar and why its assessment supports the requested value.

Incorrect characteristics and condition evidence

For incorrect property characteristics, gather the current property record, a screenshot of the disputed fact, and proof of the correct fact. Depending on the issue, that proof may include measurements, survey or plat, deed, permit records, occupancy documents, photos, or official municipal records.

For condition, damage, vacancy, demolition, or construction issues, use dated photos, contractor estimates, insurance reports, inspection notes, permits, receipts, or other documents that connect the condition to value.

Recent purchase documents

If the property sold recently, include enough documentation for the reviewer to understand price, date, parties, and whether the sale was arm's-length. Board rules specifically require disclosure of purchase price and date when a purchase occurred within three years of the lien date.

If the sale price is unusually high or low compared with the Assessor's value, be ready to explain the circumstances with documents instead of relying on the sale number alone.

Organize the packet for the forum

For the Assessor stage, make the online filing complete before submission. The residential appeals page says supporting data and documentation must be submitted concurrently with the appeal, and the online page says to submit one application by the deadline.

For the Board stage, preserve the complaint number, township close date, evidence deadline, and hearing choice. Board rules say late evidence will not be accepted except in narrow Board-requested situations, so label the packet as if it may be reviewed without a live explanation.

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