Radon Disclosure in Illinois: A Yorkville, IL Guide

Do Illinois Home Sellers Have to Test for Radon?

No. Illinois law doesn’t require sellers to test for radon, but the Illinois Radon Awareness Act requires every seller to hand the buyer a radon disclosure form and an approved information pamphlet before the buyer signs a purchase contract. If the seller already knows the home has tested high, that has to be disclosed too. Buyers routinely test anyway during the inspection period, and in Kane County, one of the EPA’s highest-risk radon zones in the state, that test carries more weight than most people realize.

By Kealan O’Neil | September 20, 2026

Radon disclosure catches sellers off guard almost every time. They read “disclosure” and assume it means “I have to test my house before I can sell it.” That’s not what the law says, and the gap between what people assume and what’s actually required is exactly where deals get complicated during attorney review.

Here’s what the radon disclosure requirement actually covers, why it matters more in Kendall and Kane County than in a lot of the state, and what typically happens when a buyer’s test comes back elevated.

What Illinois Radon Disclosure Actually Requires

The Illinois Radon Awareness Act requires sellers of most residential property to give the buyer two things before the buyer becomes bound to the contract:

• A pamphlet titled “Radon Testing Guidelines for Real Estate Transactions,” published by the Illinois Emergency Management Agency
• A completed Disclosure of Information on Radon Hazards form

That’s the whole obligation on the front end. The law doesn’t require the seller to test, and it doesn’t require a mitigation system before closing. What it does require is disclosure of any radon test results the seller already has and any known radon hazard in the home. If you tested two years ago and the number came back high, that’s a fact you disclose, whether or not you ever fixed it.

This runs alongside the separate Illinois Residential Real Property Disclosure Report, which asks sellers to disclose known material defects generally. Radon disclosure is its own statute (420 ILCS 46) with its own form, so it’s easy for a seller to hand over one disclosure packet and assume radon is covered inside it. It isn’t. Both documents need to be in the file.

Why Radon Matters More in Kendall and Kane County Than You’d Think

Radon comes from uranium breaking down in soil and rock, and it seeps into a home through the foundation. It has nothing to do with a home’s age, so a brand-new build in Grande Reserve just as easily has an elevated reading as a hundred-year-old house downtown.

The reason this is worth taking seriously here specifically:

• The Kane County Health Department places Kane County in the EPA’s Zone 1, the agency’s highest radon-potential category, with an average test result of 4.6 pCi/L against a national average of 1.3 pCi/L.
• The EPA’s action level is 4 pCi/L. At or above that number, the agency recommends fixing the home. Between 2 and 4 pCi/L, it says homeowners should still consider it.
• Illinois’s emergency management agency reported in early 2026 that radon is linked to roughly 1,200 deaths a year statewide, and that close to one in five Kendall County homes tested come back at or above the EPA’s action level, according to reporting from Shaw Local.

None of that means a home in Yorkville, Oswego, or Montgomery has a problem. Most tests come back fine. It does mean a buyer requesting a radon test isn’t being paranoid, and a seller shouldn’t be surprised when one asks. Given where Kendall and Kane County sit on the EPA’s map, I’d expect it and plan for it before a contract is even signed.

What Happens When a Buyer Asks for a Radon Test

A radon test isn’t part of the disclosure paperwork. It’s something buyers usually add on during the home inspection, either as its own test or bundled with the general inspection. A short-term test takes 48 hours and runs somewhere in the neighborhood of what any other add-on inspection service costs.

If the result comes back at or above 4 pCi/L, here’s how it typically plays out:

1. The buyer raises it during attorney review or the inspection contingency, the same window used to negotiate any other inspection finding.
2. The seller and buyer negotiate who pays for mitigation. A standard sub-slab depressurization system, the most common fix, typically runs in the $800 to $2,800 range depending on the foundation, plus a small amount to run the fan going forward.
3. The parties settle it one of three ways: the seller installs the system before closing, the seller credits the buyer at closing to handle it after, or the buyer accepts the home as-is and handles it on their own timeline.

This is the same negotiation muscle as an earnest money dispute or a low appraisal. It’s a number, and numbers get negotiated. The mistake I see sellers make is treating a radon result like a deal-killer instead of a fixable line item. A $1,500 mitigation credit on a $450,000 sale rarely blows up a deal that both sides otherwise want.

Buyers purchasing new construction shouldn’t assume they’re exempt, either. New construction removes plenty of risk from an inspection, but not this one. If you’re weighing a new build against resale in Yorkville or Montgomery, radon is one more line item to fold into that comparison, alongside things like SSA taxes that also catch new construction buyers off guard.

Common Questions About Radon in Fox Valley Home Sales

Buyers and sellers going through this for the first time usually ask some version of these questions.

Radon disclosure is a small piece of paperwork with real negotiating weight behind it, especially in a county the EPA already flags as higher risk. Whether you’re selling a home in Yorkville and want to get ahead of a buyer’s test, or you’re under contract on a home in Oswego or Montgomery and deciding what to do with an elevated result, it’s worth talking through your specific situation rather than guessing at what’s standard.

If you’re working through this for your own home in Yorkville, Oswego, Montgomery, or anywhere in the Fox Valley, I’m happy to walk you through it. Call or text Kealan at 630-425-8815.

About Kealan O’Neil
Kealan O’Neil is the Designated Managing Broker and founder of O’Neil Property Group, an independent real estate brokerage based in Yorkville, Illinois. He and his team help buyers and sellers in Yorkville, Oswego, Montgomery, and the surrounding Kendall and Kane County communities, and he owns and manages a local rental portfolio, so he approaches every decision as both a broker and an investor. Call or text Kealan at 630-425-8815.

This post is general information about real estate in the Fox Valley, not legal, tax, or financial advice. Real estate laws, tax rules, and municipal ordinances change, and how they apply depends on your specific situation. Talk with a licensed attorney, CPA, or lender before making decisions about a purchase, sale, or tax matter. O’Neil Property Group is a licensed Illinois real estate brokerage.