For Microsoft and other cloud operators, the dispute is a reminder that an AI buildout is not measured only in GPUs, megawatts and construction spending. The long-term operating economics also turn on whether generators, chillers, electrical infrastructure and other costly equipment are counted as taxable real estate—and on whether local governments keep extending incentives designed for industrial development.
The investigation identifies 18 data centers in Elk Grove Village, Northlake, Franklin Park and nearby northwest suburbs that received multimillion-dollar reductions in taxable value. Eleven also had Cook County’s Class 6b industrial incentive, while 12 held separate Illinois data-center tax benefits. The reporting calculates that the combined effect removed nearly $2 billion from the facilities’ taxable value and produced almost $100 million in projected local property-tax savings.
That headline number needs a precise reading. It is not a check written from a municipal account to Microsoft or another operator. It is a projection of taxes that would have been paid had the facilities retained the assessor’s value and had not received the incentive treatment. But the practical effect is still consequential: when governments hold their levies steady, lower equalized assessed value from one major property changes the rate charged to everyone else.
The Microsoft Azure appeal shows the valuation gap
Microsoft’s Azure facility in Northlake illustrates why this issue is becoming a core infrastructure-policy fight rather than a routine tax appeal. Illinois Answers and the Tribune report that Microsoft’s appraiser placed the site’s value at about $250 million, while Cook County Assessor Fritz Kaegi’s office argued for nearly $900 million. The Cook County Board of Review ultimately settled on about $364 million.
That is an enormous range for the same physical facility. The Assessor’s Office, through its director of valuations research David Lehman, said its figure was based in part on the property’s 2009 sale price of $182 million plus at least $650 million in later upgrades identified through permit data. The Board of Review’s final value landed much closer to the owner’s appraisal than to the assessor’s estimate, although it remained above Microsoft’s proposed valuation.
Microsoft declined comment to the Illinois Answers Project and Tribune. The reporting does not establish that Microsoft’s valuation was improper; property assessment disputes are adversarial by design, and owners are entitled to challenge an assessor’s figure. What it does establish is that the county’s current process can yield a final number hundreds of millions of dollars below the assessor’s view of the property’s value.
For residents, the important point is not which appraiser used the more persuasive spreadsheet. It is that the decision becomes part of the tax base used to support schools, park districts, municipal services and other local taxing bodies. The facility is not a generic warehouse with some racks inside it; its purpose depends on power and cooling systems that are expensive, specialized and difficult to separate from the building’s function.
Lehman’s argument, reported by Illinois Answers and the Tribune, is that data-center appeals routinely omit or discount backup generators and chillers by characterizing them as personal property rather than real estate. He has argued that data centers should be assessed by electrical capacity as well as—or instead of—conventional square-foot comparisons. That is a credible policy issue for assessors to resolve: a facility’s revenue-producing capability is constrained by power capacity, redundancy and cooling, not merely by its floor plan.
Cook County’s public assessment data distinguishes among land, building and total assessed value, but it does not by itself settle the harder question of how much specialized plant should be embedded in the building value. The lack of transparent market data compounds the problem. Data-center leases, customer commitments, power contracts and equipment configurations are often confidential, making conventional comparable-sales analysis a weak fit for an asset class whose value may rest principally in its utility infrastructure.
Class 6b is a separate decision from an assessment appeal
The nearly $100 million figure combines two mechanisms that should not be blurred together. Assessment appeals reduce a property’s value after an owner challenges the assessor’s number. Class 6b is a policy incentive approved with municipal support to encourage industrial construction, rehabilitation or reuse.
Under Cook County’s published rules, a Class 6b property is assessed at 10% for its first 10 years, then 15% in year 11 and 20% in year 12. The standard industrial assessment level is 25%. The incentive can also be renewed.
In other words, a data center can receive a lower valuation through the appeal process and then receive a lower assessment percentage through Class 6b. Those are distinct choices, made through different parts of the property-tax system, but their financial effect stacks. A low valuation narrows the starting figure; the incentive lowers the share of that figure that becomes taxable.
The Illinois Answers Project and Tribune found that five data-center complexes in Elk Grove Village had active incentives that erased more than $280 million in taxable value last year, representing about $14.5 million in tax savings. The estimated impact on the average Elk Grove Village homeowner was much smaller—about $33 annually—than in Northlake. That contrast is useful: large data-center incentives do not affect every neighboring taxpayer equally. The outcome depends on how concentrated data centers are within a town’s tax base and which taxing districts draw revenue there.
Northlake is the sharper warning. The three data centers there accounted for about 28% of the city’s tax base last year, according to the joint investigation. Without the reductions and incentives modeled by the reporters, the average homeowner’s bill would be more than $2,000 lower annually, or roughly 30%, the analysis found.
Those are modeled counterfactuals, not revised tax bills ordered by a county agency. Illinois Answers and the Tribune explain that they simulated higher assessed values, recalculated equalized assessed value and then applied the 2025 levies to estimate the resulting rates and homeowner bills. The method does not prove that every dollar forgiven would automatically become a dollar of homeowner relief; taxing bodies could make different future levy decisions. It does show the scale of exposure created when a few facilities dominate a community’s taxable value.
Illinois has already stopped taking new data-center incentive applications
The state-level benefits in this story are separate again. Illinois’ Data Center Investment Program provides sales- and-use-tax exemptions for qualifying facilities and, in some circumstances, construction wage credits. State rules required at least $250 million in investment over five years, at least 20 qualifying jobs with compensation above the county benchmark, and carbon-neutral status or an approved green-building certification.
The program was designed to make Illinois competitive for large data-center projects. Its incentives apply to equipment and purchases that can be exceptionally expensive during a buildout, including the computing, networking and operational systems required to run a hyperscale facility. Illinois’ 2024 program report says approved projects must report investment, jobs and the value of benefits received, while exemption certificates are issued in five-year increments and can last up to 20 years if compliance continues.
But the state is no longer accepting new applications. The Illinois Department of Commerce and Economic Opportunity says that, under a June 5, 2026 directive from Gov. J.B. Pritzker, it stopped processing new Data Center Investment Program applications on July 1, 2026.
That does not mean the O’Hare-area facilities identified in the investigation suddenly lost their existing state benefits. The department’s own program materials say existing certificates may be renewed in five-year increments, subject to ongoing compliance and the terms of their agreements. The practical policy question is therefore narrower and more urgent: whether Illinois and Cook County will reassess the deals already in place before renewing, extending or replacing them.
The shutdown of new applications also undercuts the claim that every current incentive is necessary to prevent data-center development from locating elsewhere. The O’Hare corridor has obvious advantages independent of tax treatment: established fiber connectivity, dense power infrastructure, industrial-zoned land and proximity to a major airport and metropolitan customer base. That does not prove incentives made no difference in individual siting decisions. It does mean officials should demand project-specific evidence before treating each renewed tax break as indispensable.
AI infrastructure needs a valuation rule that matches its physical reality
Data centers are increasingly described as software infrastructure, but their tax fights are intensely physical. A cloud region depends on substations, backup generation, switchgear, battery systems, chillers, cooling distribution and hardened buildings. If those assets can be treated as removable personal property for assessment purposes while they remain operationally integral to the facility, the tax base may fail to reflect what has actually been built.
Cook County has already shown that its assessment system can publish parcel-level values and track stages from initial assessment through Board of Review certification. The missing piece is a durable, publicly understandable methodology for hyperscale and AI-oriented facilities: how electrical capacity is valued, when equipment is a fixture, which upgrades belong in market value, and how officials test appraisals in a market with few transparent comparable transactions.
Without that framework, every major data-center assessment becomes a bespoke negotiation between companies with specialist advisers and a county trying to value assets that did not fit neatly into old industrial-property models. The Northlake Azure decision shows the cost of leaving that question unresolved: hundreds of millions of dollars can turn on definitions that residents rarely see until their own tax bills arrive.