Companies Using IIS

I've spent most of my career on crawlers, and the Server header is one of the oldest signals we read. It's also one of the easiest to lose. A domain counts on this page when its web server answers with Microsoft-IIS, usually followed by a version number. As of our October 2026 crawl that's 434,800 domains, 5th of the 70 web servers we track, and 256,439 of them match a company. Every one of those numbers is a floor, and the version number is where this profile gets useful.

Why the count is a floor

IIS 10.0 can drop the Server header with a single request-filtering attribute, removeServerHeader, which Microsoft added in that release. Put a CDN, a load balancer or an application gateway in front, and visitors see that layer's name instead. When I re-checked the top 15 rows of our company list in October, two answered with an Akamai header, though our crawler had seen IIS on both. Some large Windows estates won't show up here at all.

Sales signal: treat an IIS detection as confirmed and its absence as unknown. If an account matters, look at its application subdomains, where we find IIS far more often than on the homepage.

Growth trajectory

The chart reads 304,677 in June 2026, then 397,438, 417,636, 430,828 and 434,800 in October. Don't read the June to July jump as a Windows revival. The domain set we crawl turns over every month, with dead sites dropping out and new ones added, and our detection signals widen over time; both moved that month. Since then the monthly gain has fallen from 20,198 to 3,972. Since March 2026, 35,737 domains have dropped IIS, and about one in seven of those still show it on another hostname, so the real exits are fewer.

"IIS is a small slice of the public web, 2.96% of the servers we track, but it's still the server of the back office. Registries, forms, portals and order systems are where we keep finding it." - David Thomson, CTO at TechnologyChecker.io

Sales signal: this is a steady installed base of about 435,000 domains, not a growing one. Sell to what it runs and what it needs replaced.

Who runs IIS

The size split surprises people who think of IIS as an enterprise server. 55.97% of matched companies have 1 to 10 employees and 79.59% have 50 or fewer. The enterprise tail is still large: 6,420 companies above 1,000 staff. At those, IIS lives on applications. 39 of the 50 companies in our top list were detected on a subdomain: Boeing's surplus-sales auctions, PwC's Talent Exchange, the US State Department's passport and e-forms site, Ohio's public checkbook, Penn State's registrar. IQVIA, Gap Inc., Wesfarmers and Northwestern Medicine run it on the main site. The companies are older, too: 41.02% of matched companies were founded before 2000 and only 8.73% in the 2020s.

Sales signal: at large accounts the IIS owner is usually an application team (admissions, procurement, HR, patient registration), not the web team. Find the application first, then its owner.

Italy, Turkey and India

The United States leads with 65,713 matched companies, but the next places are unusual. India has 20,019, Italy 19,608, the United Kingdom 17,622, Brazil 16,416 and Turkey 13,846. On our jsDelivr profile the US has 12.73 companies for every Italian one; on IIS it's 3.35, and for Turkey 4.75 against 19.83. Industry is flat by comparison. IT services leads at 5.04% and software at 4.45%, and no sector reaches 5.1%. Healthcare adds up to 4.17% across hospitals and medical practices, and it's the sector where named accounts run IIS on patient-facing systems such as registration and giving forms.

Sales signal: for Windows Server migration or .NET modernisation, Italy, Turkey and India hold proportionally more IIS sites than they do jsDelivr sites. Localise there first.

No clean switching corridor

We test every server pair for switching, and only one got through. The Server header is per hostname, so one domain can legitimately show two servers: 14,431 domains show IIS and Nginx today, and 13,864 IIS and Apache. Most domains ever seen with IIS and one of these still run both, which describes a mixed setup, not a migration. OpenResty passed, and we still didn't publish it: it usually sits as a proxy or firewall in front of the origin. When that layer is added or removed the header flips, while the application behind it stays put. 83% of the IIS sites in that corridor run ASP.NET, and their page titles include "Redirecting..." and "502 Bad Gateway".

"When a Server header changes from IIS to OpenResty, the application usually hasn't moved. Someone put a proxy in front of it." - David Thomson, CTO at TechnologyChecker.io

Sales signal: don't build a "leaving IIS" list from header changes. A new proxy in front of an ASP.NET app is a security or performance project, and that's the conversation to have.

The stack: ASP.NET first

Of the 439,702 live IIS domains left after we removed for-sale and gambling pages, 83.12% run Microsoft ASP.NET and 1.3% run Blazor. Google Analytics is on 48.08%. Public JavaScript CDNs are common: cdnjs on 18.72%, jsDelivr on 13.69%, Google Hosted Libraries on 11.62%. WordPress appears on 11.69%, but the stack is read per domain, so a WordPress blog may run on a different server from the IIS application. Consent tools are thin. Cookie Control (1.99%) and Cookiebot (1.88%) lead, and OneTrust is on 0.94%.

Sales signal: none of the consent managers we chart reaches 2% of IIS domains. For consent vendors and privacy consultancies, an ASP.NET site with no consent banner is a short, specific pitch.

The version table as a prospect list

The version table further down this page is the part I'd act on. Of the 417,301 domains that announce one of the seven IIS versions, 38,612 (9.25%) report a release whose Windows Server is past the end of extended support. 34,115 of them are on IIS 8.0 or 8.5, the Windows Server 2012 generation. Microsoft ended support for those on 10 October 2023, and the last year of paid Extended Security Updates on its lifecycle pages closes on 13 October 2026. IIS 10.0 hides another deadline: Windows Server 2016 leaves extended support on 12 January 2027, and its header looks the same as 2019's or 2025's.

Sales signal: the 34,115 domains on Windows Server 2012-era IIS are the clearest upgrade and migration list in this data. Open with the support date. It's public, and the owner can check it in a minute.

Key takeaways

1. 434,800 domains, 5th of 70 web servers, and a floor, because IIS 10.0 can hide its header.

2. 83.12% of IIS domains run ASP.NET. The server follows the framework.

3. Small companies dominate (79.59% have 50 staff or fewer), while large accounts run IIS on application subdomains.

4. Italy and Turkey carry far more weight here than on a general web library such as jsDelivr.

5. 9.25% of versioned domains announce an IIS release past end of support, 34,115 of them from the Windows Server 2012 generation.

How to use this list

Use the version table to set priorities, then filter the list by company size and country. Our technology detection methods post explains how header signals are matched and scored. For the full list of 434,800 IIS domains with company, size and stack data, explore TechnologyChecker.io.