What Evidence Do You Need for a Cook County Property Tax Appeal?

Filing a property tax appeal in Cook County is only as strong as the evidence behind it. Whether you are challenging the assessed value of a single retail storefront or a multi-tenant office building, the Cook County Assessor's Office (CCAO) has specific rules governing what evidence is needed for a property tax appeal in Cook County — and failing to meet those requirements is one of the fastest ways to get your appeal dismissed. This guide walks through every major evidence category, organized by the CCAO rule that governs it, so you can submit a complete and compliant appeal package on the first try.

For a step-by-step walkthrough of the filing process itself, see our guide on how to file a property tax appeal in Cook County. This post focuses specifically on the documentation and evidence you need to assemble before you file.

Rule 12: General Evidence Requirements for All Appeals

Regardless of which appeal basis you choose — comparable sales, income approach, vacancy, or appraisal — Rule 12 of the CCAO Appeal Rules establishes baseline requirements that apply to every single filing. Missing any of these can result in your appeal being rejected before a reviewer even looks at the substance of your case.

Dated Photographs of the Subject Property

Every appeal must include dated color photographs of the subject property. These photos must have been taken within one year of the lien date (January 1 of the assessment year). The purpose is to document the property's actual physical condition as of the relevant valuation date.

If your camera or phone does not produce a visible date stamp on the image, you must complete and submit an Attestation Form certifying the date the photographs were taken. The CCAO does not accept undated photos without this attestation — even if the EXIF metadata contains a date.

Photos should clearly show:

The exterior of the building from multiple angles
The condition of the roof, walls, parking areas, and landscaping
Any visible deferred maintenance, damage, or functional obsolescence
Interior conditions if relevant to the appeal (especially for vacancy or condition-based arguments)

Non-Pro-Se Filer Photo Requirements

If you are filing through a representative — a tax consultant, attorney, or any non-pro-se filer — the requirements are more stringent. Non-pro-se filers must include dated color photographs not only of the subject property but also of every comparable property cited in the appeal. This means that if you submit five comparable sales, you need five sets of comp photos in addition to your subject property photos. Each set must meet the same dating and attestation requirements.

This rule catches many first-time filers off guard. Gathering comp photos requires either visiting each property in person or using a professional photography service. Note that Google Street View images are not acceptable as a substitute for dated photographs, a point we will revisit in the vacancy section below.

Rule 13: Sale and Purchase Documentation

If the subject property was sold within the two years preceding the lien date, you must submit sale documentation regardless of your appeal basis. This is not optional — Rule 13 applies even if you are filing an income-based or comparable-sales-based appeal. The CCAO wants to know the actual transaction price of any recently sold property under appeal.

Required documents include:

Purchase and Sale Agreement (PSA): The fully executed contract, including all amendments and addenda
Deed: The recorded deed transferring ownership
Closing Statement: The HUD-1 or closing disclosure showing the final purchase price, credits, and adjustments
PTAX-203: Required if personal property (furniture, fixtures, equipment) was included in the sale price. This form separates the real property value from personal property, which the Assessor should not be taxing

Disclosure of Buyer, Seller, and Relationships

Rule 13 also requires full disclosure of the identities of both the buyer and seller, plus any relationship between them. The CCAO is looking for arm's-length transactions — sales between unrelated parties at market-driven prices. If the sale involved related entities, a foreclosure, a 1031 exchange with a below-market component, or any other non-arm's-length factor, the CCAO needs to know. Failure to disclose a relationship can result in the appeal being dismissed and may affect future filings.

Rule 15: Comparable Sales Evidence for Cook County Appeals

The comparable sales approach is one of the most common bases for a Cook County property tax appeal, particularly for retail and industrial properties where sufficient transaction data exists. Rule 15 governs what constitutes acceptable comparable sales evidence.

You must submit a minimum of 3 comparable sales, though the CCAO recommends 5 for a stronger case. For a deeper dive into selecting the right comps, see our guide on comparable sales in property tax appeals.

Each comparable sale must include:

Property Index Number (PIN): Every comp must be identified by its 14-digit Cook County PIN. Sales without PINs will not be considered.
Sale price and date: The transaction must be recent enough to reflect current market conditions, typically within 2-3 years of the lien date
Property characteristics: Square footage, building class, age, condition, and use type — all must be reasonably similar to the subject property
Arm's-length verification: Each comp must represent a genuine market transaction. Foreclosures, related-party sales, and distressed transactions generally do not qualify unless you are specifically arguing that distressed sales reflect the market for your property type
Dated color photographs: As noted under Rule 12, non-pro-se filers must include dated photos of each comparable property

The most effective comparable sales packages include properties that are geographically close to the subject, similar in size and construction, and sold at prices per square foot that are materially lower than the Assessor's implied value for your property. A well-constructed comp set tells a clear story: the market says your property is worth less than the Assessor thinks.

Rule 16: Income-Producing Property Documentation

For commercial properties that generate rental income — office buildings, retail centers, industrial warehouses, mixed-use properties — the income approach is often the strongest appeal basis. Rule 16 sets out what the CCAO requires to evaluate an income-based appeal. The documentation burden here is heavier than for comparable sales, but the potential savings are often larger. For a comparison of when to use each method, see our analysis of the income approach vs. sales comparison for property tax appeals.

RPIE Completion in SmartFile

Before filing an income-based appeal, you must complete the Real Property Income and Expense (RPIE) form through the CCAO's SmartFile system. The RPIE collects detailed income and expense data for your property, including gross potential income, vacancy and collection losses, operating expenses by category, and net operating income. The CCAO uses this data both to evaluate your specific appeal and to calibrate its assessment models across the county.

RPIE completion is a prerequisite — if your RPIE is not on file, your income-based appeal will not be processed.

IRS Tax Schedules

You must submit IRS tax schedules for the prior 3 years. This typically means Schedule E (for individual owners reporting rental income) or the equivalent pages from a partnership or corporate return. The CCAO cross-references your reported income and expenses against the RPIE data to check for consistency. Significant discrepancies between your tax returns and your RPIE can undermine your appeal.

Lease Documentation

You must provide either complete copies of all current leases or detailed lease summaries. If providing summaries, each must include:

The parties to the lease (landlord and tenant names)
Lease type (gross, modified gross, triple net, percentage rent)
Leased square footage
Rental rates (base rent, escalations, CAM charges)
Tax responsibility clauses (who pays property taxes — landlord or tenant)
Lease term (start date, expiration, renewal options)

Affidavit Regarding Lease Party Relationships

Rule 16 requires an affidavit disclosing any relationships between the landlord and tenant parties. If a building owner leases space to a related entity at below-market or above-market rates, the CCAO needs to know. Related-party leases are not arm's-length and may be adjusted or excluded from the income analysis.

Rule 14: Appraisal Evidence Requirements

Submitting a professional appraisal can be one of the most persuasive forms of evidence in a property tax appeal, but Rule 14 imposes strict requirements on what qualifies as an acceptable appraisal.

The appraisal must be:

USPAP-compliant: Prepared in accordance with the Uniform Standards of Professional Appraisal Practice by a state-licensed or state-certified appraiser
Dated within the triennial period: The effective date of the appraisal must fall within the current reassessment cycle. An appraisal from a prior triennial period will not be accepted
PIN-inclusive: The appraisal must include the Property Index Number of both the subject property and every comparable property cited within the report

Cap Rate Requirements

If the appraisal uses an income capitalization approach, the cap rates must be derived from current market data. The CCAO is particularly attentive to this point. Appraisals that use outdated cap rates, rates from dissimilar markets, or rates that do not reflect the risk profile of the subject property will be scrutinized. Additionally, be aware of whether you are using loaded or unloaded cap rates — the Assessor typically uses unloaded cap rates (which do not include the property tax component), and submitting a loaded cap rate without adjustment can create an apples-to-oranges comparison that weakens your case.

Rule 20: Vacancy Documentation for Cook County Appeals

Vacancy appeals are a distinct category with their own documentation requirements under Rule 20. If your commercial property is partially or fully vacant, you may be able to argue for a reduced assessment based on actual occupancy conditions. For a comprehensive walkthrough, see our guide on Cook County vacancy appeals for commercial properties in 2026.

Vacancy/Occupancy Affidavit

Every vacancy appeal must include a completed Vacancy/Occupancy Affidavit. This sworn document certifies the occupancy status of the property as of the lien date, including which spaces are occupied, which are vacant, and for how long.

Photograph Requirements for Vacancy

Vacancy appeals require dated photographs of both the interior and exterior of the property. This is more demanding than the general Rule 12 photo requirement. The interior photos must show the vacant spaces — empty tenant suites, unused warehouse bays, shuttered retail storefronts. The purpose is to visually confirm that the spaces claimed as vacant are genuinely unoccupied.

A critical point: Google Street View images are not acceptable for vacancy appeals. The CCAO has explicitly rejected Street View screenshots because they cannot be independently dated and do not show interior conditions. You must take your own dated photographs or hire a photographer to document the property.

Category-Specific Vacancy Documentation

Depending on the reason for vacancy, the CCAO requires additional supporting documents:

Market vacancy (space available for lease): Current rent roll showing occupied and vacant spaces, marketing materials, listing agreements, and evidence of leasing efforts
Renovation vacancy: Building permits, contractor agreements, architectural plans, and a timeline showing when the space was taken offline and when it is expected to return to service
Casualty vacancy (fire, flood, structural damage): Insurance claims, damage assessment reports, fire department or building department reports, and photographic evidence of the damage

Rule 9: Anonymization Requirements for Practitioners

Rule 9 introduces a documentation requirement that applies specifically to practitioners — attorneys, consultants, and other non-pro-se filers. Under this rule, practitioners must submit two complete sets of appeal documents:

An anonymized set: All non-public personal information (NPPI) must be redacted. This includes Social Security numbers, bank account numbers, and other sensitive data that may appear in leases, tax returns, or closing documents
A non-anonymized set: The complete, unredacted documents for the CCAO's internal review

The anonymized set may be made available to other parties (such as taxing districts that wish to review appeals), while the non-anonymized set remains confidential. Failing to submit both sets — or submitting an anonymized set with incomplete redactions — can delay or derail your appeal.

Common Evidence Mistakes That Get Appeals Rejected

Even experienced filers make evidence errors that weaken or disqualify their appeals. Here are the most common mistakes the CCAO sees:

Blurry or Undated Photographs

Photos that are out of focus, too dark to interpret, or missing date stamps (without an Attestation Form) are the single most common reason appeals are returned for correction. Take clear, well-lit photos and verify the date stamp or attestation before filing.

Missing NPPI Redaction

Practitioners who forget to redact Social Security numbers, EINs, or bank account numbers from the anonymized document set create compliance problems. Review every page of your anonymized set before submission. A single unredacted SSN on a lease guarantee page can require you to resubmit the entire package.

Google Maps or Street View Photos for Vacancy Claims

This is a recurring issue. Property owners or their representatives submit Google Maps screenshots or Street View images as evidence of vacancy or property condition. The CCAO does not accept these. You need original, dated photographs taken by someone with direct knowledge of the property. This applies to both subject property photos and comparable property photos.

Using Loaded Cap Rates When the Assessor Uses Unloaded

This technical error is surprisingly common in income-based appeals. A loaded cap rate includes the property tax component in the capitalization rate, while an unloaded cap rate excludes it. The Assessor's income models typically use unloaded cap rates. If you submit an appraisal or income analysis using a loaded cap rate without adjusting, your indicated value will appear artificially lower than it should on an apples-to-apples basis, and the CCAO reviewer will catch the discrepancy. Make sure your cap rate methodology matches the Assessor's framework, or clearly explain and reconcile any differences.

Insufficient Comparable Sales

Submitting only 1-2 comps when the minimum is 3 will get your appeal rejected on procedural grounds before the merits are even considered. Submit at least 3, aim for 5, and make sure each comp has a PIN, a verified sale price, and supporting photos.

Building a Complete Evidence Package: A Checklist

Before submitting your appeal, run through this checklist to make sure your package is complete:

Dated color photographs of the subject property (within 1 year of lien date)
Attestation Form if photos lack visible date stamps
Photos of all comparable properties (required for non-pro-se filers)
Sale documentation if property sold within 2 years (PSA, deed, closing statement, PTAX-203 if applicable)
Buyer/seller identity and relationship disclosure
At least 3 comparable sales with PINs (5 recommended)
RPIE completed in SmartFile (for income-based appeals)
IRS tax schedules for prior 3 years (for income-based appeals)
Complete lease copies or detailed summaries (for income-based appeals)
Lease party relationship affidavit (for income-based appeals)
USPAP-compliant appraisal with PINs and current cap rates (if submitting an appraisal)
Vacancy/Occupancy Affidavit (for vacancy appeals)
Interior and exterior dated photos (for vacancy appeals)
Category-specific vacancy documentation (rent roll, permits, or damage reports)
Both anonymized and non-anonymized document sets (for practitioners)
All NPPI properly redacted in the anonymized set

How TaxRival Handles Evidence for You

Assembling a complete, rule-compliant evidence package is one of the most time-consuming parts of a Cook County property tax appeal. At TaxRival, we handle the entire evidence-gathering and documentation process for our clients. Our team compiles comparable sales with verified PINs and photographs, prepares income analyses using the Assessor's own methodology, ensures RPIE compliance, and submits both anonymized and non-anonymized document sets that meet every CCAO requirement.

Our fee is 25% of first-year tax savings — below the industry standard of 30-33% — and you pay nothing if we do not reduce your assessment. Visit taxrival.com to check your property and see your estimated savings.