By: Mary Kate Fitzgerald | Fitzgerald Law Group, P.C.
Property owners frequently receive a reassessment notice, review the stated value, and reasonably presume that it is accurate. That assumption is understandable. Assessing officials utilize mass appraisal systems, rely on extensive market data, and employ trained analysts supported by increasingly sophisticated valuation models. From the outside, the process appears both comprehensive and precise.
In practice, however, assessment is not an exact science. It is an opinion of value—derived from generalized data, standardized modeling, and a series of necessary assumptions applied across broad categories of property. By its nature, this process often lacks the property-specific detail required to capture the unique characteristics, conditions and economic realities affecting an individual asset.
As a result, assessments may deviate materially from fair market value. The complexity arises not from a single issue, but from the interplay of valuation methodologies, data selection, statutory requirements, and judgment calls made within a constrained administrative framework. A clear understanding of why assessments are inherently imprecise—and the specific issues that become points of dispute between taxpayers, assessing officials, and intervening taxing bodies—is essential to effectively evaluating and pursuing a property tax appeal.
Part One: Why Assessment Is Inherently Complicated
1. Valuation Is Not an Exact Science
Two equally qualified, equally experienced appraisers can look at the same property, review the same sales data, and arrive at materially different conclusions. This is not incompetence — it is the nature of real estate valuation. Methodology matters enormously. Whether an appraiser relies on the sales comparison approach, the income approach, or the cost approach, and how they weight each, will drive the result. The assumptions embedded in a capitalization rate, the adjustments applied to comparable sales, the depreciation schedule used for a cost analysis — each is a professional judgment, and each introduces variability.
For tax appeal attorneys, this reality is liberating. The assessor’s value is not the truth. It is one opinion. Our job is to present a more persuasive opinion, supported by better data and sounder methodology.
2. Mass Appraisal Overlooks the Details
Assessors do not appraise each property individually every year. They use mass appraisal — statistical models applied across broad property classes to estimate value for hundreds of thousands of parcels simultaneously every three years in Cook County. These models are calibrated to the average, and the average is, by definition, wrong for properties that deviate from it. Mass appraisal considers a property’s value from a macro-level, but your property needs to be considered from a micro-level.
Your property may have deferred maintenance, functional obsolescence, an unusual floor plan, a location disadvantage, environmental contamination, or a dozen other features that reduce its market value below what the model predicts. The model does not know this. It knows square footage, year built, property class, and perhaps a handful of other variables. The gap between the model’s assumptions and your property’s reality is where appeals are won.
3. Illinois Law Focuses on Value in Exchange
This point is specific to Illinois but reflects a principle with national relevance. Under Illinois law, property is assessed based on its value in exchange — what a willing buyer would pay a willing seller in an arm’s-length transaction. The law does not assess the going-concern value of a business operating on the property. It does not assess the value of trade fixtures, equipment, inventory, or intangible assets like brand value, assembled workforce, or customer relationships.
This distinction becomes critical for operating properties: hotels, restaurants, car washes, assisted living facilities, data centers, and similar special-purpose real estate. Assessors frequently make the mistake of capturing business value in the real estate assessment. A skilled advocate must identify and strip out those non-real-estate components to arrive at a defensible taxable value.
4. Market Conditions Change Rapidly
Assessment cycles create a structural lag between market reality and assessed value. In Illinois, assessments are supposed to reflect market conditions as of January 1 of the assessment year — but the data underlying those assessments is inevitably backward-looking. When markets turn down sharply, as they did during the financial crisis and again
during the early stages of the COVID pandemic, assessed values frequently overshoot actual market values by wide margins.
Conversely, in rising markets, assessors sometimes attempt to project values upward using data they do not fully possess. Either direction creates opportunity for the taxpayer who is paying attention. The assessment date is not a technicality — it is the legal anchor for the entire valuation analysis, and we use it rigorously.
5. Uniformity Matters as Much as Accuracy
Illinois taxpayers have a constitutional right to uniform treatment. This is independent of the right to be assessed at fair market value. Even if your property’s assessed value happens to be correct in isolation, you may have a strong uniformity appeal if comparable properties in your area are assessed at lower unit values.
Appeals can be won for properties where it is assessed at precisely fair market value because the evidence showed that similar properties were systematically assessed at lower levels. Uniformity is a powerful and underutilized tool, particularly in jurisdictions where assessment practices vary significantly across property classes.
6. Specialized Properties Create Legitimate Disputes
Not every property fits neatly into a standard valuation framework. Special-use properties —sports arenas, chemical plants, data centers — present genuine methodological challenges. When there are few or no comparable sales, how do you establish market value? The answer often requires creative application of the income or cost approach, and reasonable appraisers frequently disagree.
These cases tend to generate the largest dollar disputes and the most contentious litigation. The assessor’s position is often defensible in the abstract; it is the tax appeal attorney’s job to demonstrate that an alternative methodology better reflects market reality for that specific property type.
7. Incentives and Classification Issues Matter
Illinois offers a complex array of property tax incentives. Misclassification, failure to apply an available incentive, or improper termination of an existing incentive can result in significant overvaluation. A detailed review of the Assessor’s data against existing surveys and an in-person inspection of the property will often reveal errors. Incentive eligibility should be reviewed as a matter of course for any new development because the upside when an error is found can be substantial.
Part Two: What the Parties Argue About
When an assessment is contested, the dispute narrows to a set of recurring technical issues. Understanding these issues — and having strong opinions about them — is what separates effective advocates from those who simply submit a competing appraisal and hope for the best.
The Appraisal Date
Whether an appraisal must be dated as of January 1 of the assessment year is not merely a technical question — it determines the entire universe of relevant market evidence. Appraisers who use data from the wrong time period, even slightly, give the opposing party a legitimate methodological objection. We hold our experts to strict compliance and scrutinize the assessor’s evidence for the same lapses.
Comparable Sales — Selection and Weighting
The selection of comparable sales is where most residential and many commercial appeals are actually won or lost. Which sales are truly comparable? What adjustments are appropriate for size, age, condition, location, and time of sale? When comparable sales are sparse, how far do you expand the search, and what discount do you apply for the distance?
These questions do not have formulaic answers. They require judgment, market knowledge, and the ability to articulate and defend your choices before a skeptical board or court.
Leased Fee vs. Fee Simple
For income-producing properties, one of the most consequential methodological choices is whether to value the property in its leased fee state — i.e., as encumbered by existing leases — or at its fee simple market value, as if vacant and available. This distinction can produce dramatically different results when a property is leased significantly above or below market.
Illinois courts have not always spoken with one voice on this issue. The answer may depend on property type, lease terms, and the specific legal framework applicable to the assessment. Understanding the current state of the law and positioning your case accordingly is essential.
Distressed Sales — Bankruptcy and REO
When a market lacks arm’s-length sales, parties frequently argue over whether distressed transactions — foreclosure sales, REO dispositions, bankruptcy liquidations — should be included in the comparable sales analysis. Assessors typically want to exclude them when they are low; taxpayers typically want to include them for the same reason.
The legal standard in most jurisdictions focuses on whether the transaction was truly arm’s-length and whether both parties were acting without compulsion. This is a fact-intensive inquiry, and the answer is rarely obvious.
Sale-Leasebacks
A sale-leaseback occurs when an owner sells its property and simultaneously leases it back from the buyer. These transactions generate a recorded sale price — but that price may reflect the financing economics of the transaction as much as, or more than, the property’s standalone market value. Whether a sale-leaseback price is a reliable indicator of market value is one of the most litigated issues in commercial property tax, and the answer often turns on the specific lease terms and the financing environment at the time of the transaction.
Build-to-Suit Transactions
When a property is constructed to the specifications of a particular tenant, the resulting sale price — if the property is sold — may reflect the value to that specific user rather than the broader market. A distribution center built to a particular retailer’s exact specifications, with custom dock heights, clear heights, and column spacing, may not be replicable at the same cost but may also not be saleable to the broader market at that price. Build-to-suit sales require careful analysis before they can be used as comparables.
Vacant vs. Occupied Sales
Should the sale of a vacant property be used as a comparable to value an occupied one? The answer depends on whether the vacancy reflects a temporary market condition or a fundamental difference in property utility. In a weak market with high vacancy, using occupied sales may overstate value; using vacant sales may better reflect current market reality. This is a recurring battleground in retail and office assessment appeals.
Zoning and Legal Restrictions
Deed restrictions, conservation easements, historic preservation requirements, and zoning limitations can all reduce the range of uses available to a property and, therefore, its market value. Assessors do not always account for these constraints adequately. A careful review of title and zoning is a standard part of our due diligence on any significant commercial appeal.
Single-Tenant vs. Multi-Tenant Analysis
A single-tenant net-leased property and a multi-tenant property in the same submarket may look superficially similar but present very different risk profiles to investors. Single-tenant properties carry concentration risk; multi-tenant properties offer diversification but more management complexity. Using one as a comparable for the other without appropriate adjustment is a methodological error that we frequently identify in the assessor’s analysis.
Lease Conditions — Concessions, Renewals, and Credit
In the income approach, the lease is everything. Above-market or below-market rent, free rent concessions, tenant improvement allowances, renewal options, and the creditworthiness of the tenant all affect value. Assessors often use contract rent without investigating whether it reflects market conditions, or apply a market cap rate to a lease that carries above-market credit risk or below-market rent. These errors, identified and documented by a competent appraiser, are the basis for many of our most successful appeals.
The “Dark Store” Debate
Few issues in property tax law have generated more controversy in recent years than the “dark store” theory applicable to big-box retail. The argument, at its core, is that an occupied Walmart or Home Depot should be valued as if it were vacant and available for sale — because the only buyers for those properties, if they ever became available, would likely be users other than the current occupant, and those buyers would apply significant discounts for the functional and locational limitations built into a single-tenant retail box.
Assessors and taxing bodies have fought this theory aggressively, arguing that it ignores the obvious value created by occupancy. Courts across the country have reached different conclusions. In Illinois, the debate continues to evolve. Understanding the current state of the case law and structuring your appraisal accordingly is critical for any taxpayer with big-box retail exposure.
Incentives and Value
Finally, should the existence of a tax incentive — a 6b incentive, a TIF district, an Enterprise Zone abatement — affect the assessed value of the underlying real estate? The answer is nuanced. In some cases, the incentive is reflected in the income stream and therefore in the value; in others, it is a government benefit that should not be capitalized into the assessment. Getting this analysis right matters both for the appeal and for compliance with the incentive’s reporting requirements.
The Takeaways
There are two principles underlying virtually every successful property tax appeal:
The devil is in the details. General arguments about market conditions rarely move assessment boards. Specific facts — documented maintenance issues, identified comparables, demonstrated lease concessions — do.
Weight, not admissibility, is the battlefield. Most appraisal evidence is technically admissible. The fight is over whose evidence is more persuasive — better data, sounder methodology, more credible expert witnesses.
If you have received an assessment notice that you believe does not reflect the true market value of your property, the time to act is now. Assessment appeal deadlines are strict and unforgiving, and the cost of inaction is paid every year, not just once.
This article is intended for general informational purposes and does not constitute legal advice. Assessment law varies significantly by jurisdiction. Consult a qualified property tax attorney regarding your specific situation. © 2026 Fitzgerald Law Group, P.C. All rights reserved.