By Harsha N Hegde
Why do Cook County Assessor appeals fail to produce a reduction? We analyzed 474,768 Assessor appeals that received no assessed-value reduction from tax years 2021 through 2025. The public records assign a primary reason code to each result. One reason overwhelmingly dominated: the Assessor’s market analysis and analysis of comparable properties supported the existing assessment. This explanation, recorded as reason code 49, appeared in 94.90% of all no-reduction decisions. Its share was almost identical for appeals filed by property owners without an agent and appeals associated with an agent.
Nearly 95% received the same reason
Reason code 49 reads:
This is a result of a market analysis of your property as well as an analysis of comparable properties.
Of the 474,768 no-reduction appeal results, 450,552 carried this as the primary reason.
| Filer type | Appeals with no reduction | Code 49 decisions | Share coded 49 |
|---|---|---|---|
| DIY / no agent | 174,246 | 165,219 | 94.82% |
| Agent | 300,522 | 285,333 | 94.95% |
| Total | 474,768 | 450,552 | 94.90% |
The difference between DIY and agent-filed appeals was only 0.13 percentage points. That does not mean DIY and agent appeals had the same success rate or received the same reductions overall. This dataset includes only appeals that did not receive a reduction. It tells us how the Assessor categorized unsuccessful results, not whether hiring an agent improved the chance or size of a reduction. Our separate analysis compares DIY and agent appeal outcomes in Cook County.
No-reduction results by year
Code 49 accounted for more than 92% of no-reduction decisions in every year analyzed.
| Tax year | DIY no-reduction appeals | DIY coded 49 | Agent no-reduction appeals | Agent coded 49 |
|---|---|---|---|---|
| 2021 | 28,641 | 96.95% | 53,223 | 96.99% |
| 2022 | 32,506 | 97.52% | 60,956 | 97.78% |
| 2023 | 39,239 | 95.68% | 63,598 | 95.74% |
| 2024 | 45,317 | 92.02% | 69,743 | 92.07% |
| 2025 | 28,543 | 92.87% | 53,002 | 92.47% |
The pattern was remarkably consistent between the two filer groups. Their annual code 49 shares were within half a percentage point of each other in all five years. The share declined in 2024 and 2025. That does not necessarily mean the Assessor changed how it evaluated comparable properties. The main visible change was increased use of reason code 27A, which relates to the property’s actual sale transaction.
Recent sales were the second-largest reason
Reason code 27A reads:
This is due to an analysis of the actual sale transaction of the property.
It was assigned to 15,670 no-reduction decisions.
| Filer type | Code 27A decisions | Share of no-reduction appeals |
|---|---|---|
| DIY / no agent | 5,880 | 3.37% |
| Agent | 9,790 | 3.26% |
| Total | 15,670 | 3.30% |
Use of this code increased substantially in the last two years of the analysis.
| Tax year | DIY code 27A | Agent code 27A | Total |
|---|---|---|---|
| 2021 | 0 | 0 | 0 |
| 2022 | 111 | 263 | 374 |
| 2023 | 928 | 1,571 | 2,499 |
| 2024 | 3,208 | 4,801 | 8,009 |
| 2025 | 1,633 | 3,155 | 4,788 |
The zero count in 2021 reflects the reason-code structure in the data. A similar sale-analysis description appeared under code 27 that year. Because code definitions and usage can change, comparisons across years require caution. The broader point is straightforward: when a property had a relevant sale, that transaction sometimes became the Assessor’s stated basis for leaving the assessment unchanged.
Other valuation-related reasons
Almost all other frequently used codes also concerned valuation, uniformity, property characteristics, or appraisals.
Codes 16 and 17: Uniformity with comparable properties
Code 16 says the result was due to the property’s uniformity with comparable properties. Code 17 says the same but adds that the analysis included an update to the property’s characteristics. Together, these codes appeared in:
- 1,487 DIY no-reduction decisions
- 1,426 agent no-reduction decisions
- 2,913 decisions overall
These codes suggest that the Assessor concluded the assessment was already aligned with similar properties, including cases where a characteristic was updated but no lower value was warranted.
Codes 48 and 48A: Submitted appraisals
These descriptions say the Assessor considered a submitted appraisal along with comparable properties or recent comparable sales.
| Filer type | Codes 48 and 48A | Share of no-reduction appeals |
|---|---|---|
| DIY / no agent | 667 | 0.38% |
| Agent | 2,624 | 0.87% |
| Total | 3,291 | 0.69% |
The higher count among agent-filed appeals may reflect differences in property types, cases, or evidence. The results data cannot establish the cause. It also does not show why an appraisal failed to support a reduction. The reason code does not disclose the appraisal’s value conclusion, effective date, selected sales, adjustments, or the Assessor’s competing analysis.
Code 79B: Multi-improvement property analysis
Code 79B says a market and comparable analysis of a multi-improvement property concluded that a value change was not in order. It appeared in 128 DIY and 362 agent-filed no-reduction decisions, only 0.10% of the combined total.
Were many appeals rejected for missing evidence?
Not according to the recorded primary reason codes. The dataset includes descriptions such as:
- Lack of data submitted for review
- Insufficient data submitted for review
- Insufficient evidence to substantiate a field check
- No evidence warranting a field inspection
- Missing or incomplete sale documents
- Missing or incomplete representative authorization
- Failure to follow an official Assessor rule
But these explicit documentation and procedural codes accounted for only a small fraction of no-reduction results. For example, codes 18 and 19, which cite a lack of or insufficient submitted data, appeared in 105 DIY cases and 106 agent-filed cases. Together, that was about 0.04% of the 474,768 decisions. This does not prove that evidence quality was unimportant. Code 49 is broad enough to include cases with strong evidence, weak evidence, poorly selected comparables, or no owner-selected comparables. It gives the Assessor’s stated conclusion, not a detailed account of how the evidence performed.
What code 49 does and does not tell the property owner
Code 49 tells the owner that the existing assessment survived the Assessor’s market and comparable-property review. It does not reveal:
- Which comparable properties the Assessor considered
- Whether the Assessor used the comparables submitted by the appellant
- How differences in size, age, condition, class, location, or amenities were treated
- Whether the argument was evaluated primarily as overvaluation, lack of uniformity, or both
- What value the analyst considered supportable
- How close the submitted evidence came to justifying a reduction
“Comparable analysis” is therefore a category of explanation, not a detailed rebuttal of the appeal.
What the DIY and agent comparison shows
The distributions for unsuccessful DIY and agent-filed appeals were strikingly similar. Both groups had:
- About 95% of results coded as market and comparable analysis
- About 3.3% coded as analysis of the property’s actual sale
- The remaining roughly 1.8% spread across appraisal, uniformity, property-characteristic, documentation, inspection, and other reasons
This suggests that the Assessor used the same broad framework when recording why appeals received no reduction, regardless of whether an agent was identified. It does not prove that the underlying cases were comparable. Agent-filed appeals may differ from DIY appeals by property type, assessed value, complexity, evidence, geography, or the owner’s willingness to pay for representation. Without controlling for those differences, the reason codes cannot determine whether agents were more effective.
What property owners can learn from these results
The data supports three practical observations.
1. Most unsuccessful appeals were decided on valuation grounds
The recorded primary reason was rarely a missed form or an explicit lack of documentation. In most cases, the Assessor said its market or comparable analysis supported the existing assessment.
2. Providing comparables does not guarantee a reduction
A comparable helps only if it supports a lower defensible value. Similarity, neighborhood, property class, physical characteristics, assessment level, sale conditions, and the valuation date all matter.
For a lack-of-uniformity claim, the question is whether comparable properties are assessed at a lower level. For an overvaluation claim, the question is whether market evidence supports a lower estimated market value. Mixing the two without a clear requested value can weaken the presentation. Choosing the right set of comparable properties gives your appeal a stronger evidentiary basis. CookCountyAppeal.tax identifies relevant comparables and uses them to estimate a defensible potential reduction. Check your potential reduction for free.
Learn more about building a lack-of-uniformity property tax appeal.
3. A no-change code does not explain the entire decision
The descriptions are too broad to diagnose an individual appeal. A property owner cannot infer from code 49 alone that the Assessor ignored the evidence, selected better comparables, rejected a particular adjustment, or found the requested value unreasonable. If the assessment still appears excessive, the next filing should improve the evidentiary argument instead of merely resubmitting the same list of properties.
Assessor results are not Board of Review results
A no-reduction result from the Cook County Assessor is not a Board of Review decision. The Board of Review is a separate appeal stage with its own procedures and decision data. Our analysis of Cook County Board of Review no-change decisions found a different distribution of recorded reasons. Conclusions about Assessor decisions should not automatically be applied to Board of Review outcomes. For property owners considering the next stage, see our guide to appealing property taxes in Cook County.
Data and methodology
This analysis uses Cook County Assessor appeal-decision records for tax years 2021 through 2025. It includes appeals where the final Assessor total assessed value was equal to the original total assessed value, meaning the appeal produced no assessed-value reduction. Appeals were grouped as follows:
- DIY / no agent: No agent was identified in the appeal record.
- Agent: An agent was identified in the appeal record.
The analysis counts the first or primary recorded reason code. An appeal may contain additional context that is not represented by that code. The data does not include the complete evidence, the analyst’s work papers, or a controlled comparison of otherwise similar DIY and agent-filed cases. Reason codes are administrative categories, and their wording or usage may change over time. The 2025 totals may also evolve as Cook County refreshes its public records. The findings describe how no-reduction decisions were recorded. They do not establish why a specific appeal failed or which filing method caused a particular outcome.