Buying a Home in Illinois? What to Know About Radon Testing

Illinois sits entirely within EPA Zone 1 -- the highest-risk designation for radon gas. That means the state's predicted average indoor radon level exceeds 4.0 pCi/L, the EPA's recommended action level. If you're buying a home here, radon testing isn't optional. It's one of the most important inspections you can schedule.

Why Illinois Has Such High Radon Levels

The geology underneath Illinois is a big part of the story. Glacial deposits across the state contain uranium-bearing minerals that naturally decay into radon gas. That gas migrates upward through soil and enters homes through foundation cracks, gaps around pipes, sump pits, and construction joints. The flat terrain and deep soil layers across central and northern Illinois create conditions where radon accumulates readily beneath structures.

According to EPA data, the average indoor radon concentration in Illinois homes is roughly 4.4 pCi/L -- already above the action level. Some counties, particularly in the northern and central parts of the state, regularly see readings well above that. The Illinois Emergency Management Agency (IEMA), which oversees the state's radon program, has tracked these patterns for decades.

What the Law Says About Disclosure

Illinois is one of the few states with a specific radon disclosure statute. The Illinois Radon Awareness Act requires sellers to provide buyers with information about radon, including any known test results and mitigation history. This doesn't mean every seller has tested -- many haven't. But if testing has been done, they're legally required to share the results.

This is where it gets practical for buyers. Even if the seller hands over a clean disclosure form, that doesn't mean the home is safe. It means no one has tested, or the seller isn't aware of a problem. That's a very different thing. Always order your own test. For a thorough walkthrough of how testing works, see our complete radon testing guide.

How Testing Works During a Home Purchase

The standard approach is a short-term test, typically lasting 48 to 96 hours. A certified tester places a continuous radon monitor (CRM) or charcoal test device in the lowest livable area of the home -- usually the basement. During the test, windows and exterior doors should stay closed except for normal entry and exit.

Most professional testers in Illinois charge between $100 and $200 for a short-term test with results. Some home inspectors bundle radon testing with the general inspection for a combined fee. Either way, make sure whoever performs the test holds current IEMA or NRPP/NRSB credentials. A test from an uncertified person may not hold up in negotiations.

If you want to compare local testing professionals, our Illinois radon page lists certified contractors by region.

Timing Matters

Schedule the radon test as early as possible in your inspection period. Results take a minimum of two days, and if levels come back high, you'll need time to negotiate before your contingency deadline. Don't leave this for the last week before closing.

What Happens if the Test Comes Back High

A result at or above 4.0 pCi/L means the EPA recommends action. According to the EPA, radon is the second leading cause of lung cancer in the United States, responsible for an estimated 21,000 deaths per year. That's not a scare tactic -- it's the public health data.

The good news: radon mitigation works. A properly installed active soil depressurization system can reduce indoor levels by 80% to 99% in most homes. Installation typically takes one day and costs between $800 and $2,500, depending on the home's foundation type and layout. For detailed pricing breakdown, check our mitigation cost guide.

Negotiation Strategies for Buyers

You have several options when radon levels are elevated:

• Ask the seller to install a mitigation system before closing, with a post-mitigation test confirming results below 4.0 pCi/L.
• Request a closing credit equal to the estimated mitigation cost so you can hire your own contractor after closing.
• Negotiate a price reduction to cover mitigation expenses.

Most sellers in Illinois are familiar with radon -- the disclosure requirement means it comes up in virtually every transaction. A reasonable seller will work with you. An unreasonable one is telling you something about how they handle problems.

Should You Still Buy a Home With High Radon?

Absolutely. Elevated radon is not a reason to walk away from an otherwise good home. It's a solvable problem with proven technology. Thousands of Illinois homes have mitigation systems running right now, quietly keeping indoor air safe.

What matters is that you know about the issue before you close and that the cost of mitigation is factored into your purchase. A home with a documented mitigation system and a clean post-test is actually in better shape than a home that's never been tested at all.

After You Move In

Whether you bought a home with an existing system or had one installed during the purchase, long-term monitoring is smart. The EPA recommends retesting every two years, or after any major renovation that changes the home's air pressure dynamics. If your home has a mitigation system, check the system's manometer regularly to confirm the fan is running.

For help finding certified testing and mitigation professionals anywhere in the state, visit radon testing near me. If your results come back elevated and you need a mitigation contractor, start with our directory to find someone with verified credentials.

FAQ

Can I do a radon test myself during a home purchase?

You can, but most real estate transactions require a test performed by a certified professional. Self-test results may not be accepted during negotiations or by lenders.

Does Illinois require radon mitigation before selling a home?

No. The state requires disclosure of known radon information, but there is no mandate to mitigate. The decision to fix is between buyer and seller during negotiations.

Is radon worse in basements?

Radon concentrations are typically highest in the lowest level of a home because that's where soil gas enters. Upper floors usually have lower levels, but they can still be elevated in some homes.