What Is a Rule 15 Appeal in Cook County? (And How to File One)

When you appeal your Cook County property tax assessment, the strongest argument you can make isn't an opinion about what your home is worth — it's hard data from recent sales of comparable properties. That data is called Rule 15 evidence, and it's the foundation of most successful appeals.

What Is Rule 15?

Rule 15 refers to a rule of the Cook County Assessor's Office that governs how comparable sales can be used as evidence in an appeal. Specifically, it allows homeowners to submit data from recent arm's-length sales of similar properties to argue their home is over-assessed.

The logic is straightforward: if three similar homes in your neighborhood sold in the last 12 months for $350,000, but your assessment implies a market value of $420,000, you have a strong argument that the Assessor got it wrong.

Why Comparable Sales Are the Gold Standard

Cook County assessments are supposed to reflect 10% of your property's fair market value. The best evidence of market value is what buyers actually paid for similar homes in the same area.

Other arguments exist — unequal assessment (comparing your assessed value to neighbors'), or an error in the property's characteristics (wrong square footage, wrong lot size) — but comparable sales are widely considered the most persuasive evidence at both the Assessor level and the Board of Review.

What Makes a Good Comparable?

Not every recent sale qualifies. Good Rule 15 comparables should be:

• Recent — typically within 12 months of your assessment date, ideally within 6
• Arm's-length — normal market sales between unrelated buyers and sellers (not foreclosures, short sales, or family transfers)
• Similar — same general property type (single-family, condo), similar size, similar age, same township
• Proximate — within your neighborhood or close by

The Assessor's Office and Board of Review will scrutinize your comparables. Weaker ones (too old, too different in size) can hurt your case.

How Many Comparables Do You Need?

Three to five solid comparables is typically enough to make a compelling case. More isn't always better — five strong comparables beat ten mediocre ones.

How to Find Comparable Sales

Option 1: Cook County Assessor's website. The CCAO site has a property search tool that shows recent sales in any area. Search by neighborhood or township.

Option 2: Zillow or Redfin. Filter for recently sold homes similar to yours. Note: these pull from MLS data and may have slight delays.

Option 3: Your county recorder. All real estate transactions are recorded publicly. This is the authoritative source but requires more digging.

Option 4: Let OverTaxed IL do it. Our system automatically pulls comparable sales data for your address, evaluates whether you're over-assessed, and generates a Rule 15-compliant appeal packet — the same analysis tax attorneys charge $300–500 for.

What to Include in Your Rule 15 Submission

When you file, your comparables package should include:

1. The address and PIN of each comparable property
2. The sale price and sale date
3. Key property characteristics (square footage, bedrooms, lot size)
4. A brief explanation of why each property is comparable to yours

The Assessor's Office has standardized forms for this. At the Board of Review level, there's a specific comparable grid format they require.

Don't Wait to File

Rule 15 evidence only works if you submit it on time. Each township has its own filing window — and once it closes, you're waiting another year.

Start your free check at OverTaxed IL — enter your address and we'll instantly pull your assessment data, find recent comparable sales, and show you whether you have grounds to appeal. If you do, we'll generate your complete appeal packet automatically.

The process tax attorneys charge hundreds for, done in minutes.