Indiana Radon Levels by County — EPA Zone Map

March 2, 2026

Indiana is one of the highest-radon states in the country. The EPA estimates that roughly 1 in 3 Indiana homes has indoor radon levels above the action level of 4 pCi/L. Understanding your county’s risk level is the first step — but it doesn’t replace testing your specific home.

How EPA Radon Zones Work

The EPA divides every U.S. county into one of three radon zones based on predicted average indoor radon levels:

Indiana has no Zone 3 counties. Every county in Indiana is either Zone 1 (high risk) or Zone 2 (moderate risk).

Why Indiana Radon Levels Are So High

Indiana’s elevated radon levels stem from its geology. Much of the state sits on glacial till — rock, soil, and sediment deposited by retreating glaciers during the last ice age. This glacial material is rich in uranium and radium, the parent elements of radon.

As uranium in the soil decays, it produces radium. Radium decays into radon gas, which seeps upward through soil and into homes through foundation cracks, sump pits, utility penetrations, and crawl spaces.

Central and northern Indiana — which sit on the thickest glacial deposits — have the highest radon concentrations. Southern Indiana, where bedrock is closer to the surface and glacial deposits are thinner, tends toward Zone 2.

Zone 1 Counties — High Risk

The following Indiana counties are designated EPA Zone 1, meaning the predicted average indoor radon level exceeds 4 pCi/L. Testing and mitigation are strongly recommended for all homes in these counties.

Zone 1 counties include: Adams, Allen, Bartholomew, Benton, Blackford, Boone, Carroll, Cass, Clay, Clinton, Decatur, DeKalb, Delaware, Elkhart, Fayette, Fountain, Franklin, Fulton, Grant, Hamilton, Hancock, Hendricks, Henry, Howard, Huntington, Jasper, Jay, Johnson, Kosciusko, LaGrange, Lake, LaPorte, Madison, Marion, Marshall, Miami, Montgomery, Morgan, Newton, Noble, Parke, Porter, Pulaski, Putnam, Randolph, Rush, Shelby, St. Joseph, Starke, Steuben, Sullivan, Tippecanoe, Tipton, Union, Vermillion, Vigo, Wabash, Warren, Wayne, Wells, White, Whitley

Zone 2 Counties — Moderate Risk

These counties have predicted average levels between 2–4 pCi/L. Testing is still recommended — individual homes can test significantly above the Zone 2 average.

Zone 2 counties include: Brown, Clark, Crawford, Daviess, Dearborn, Dubois, Floyd, Gibson, Greene, Harrison, Jackson, Jefferson, Jennings, Knox, Lawrence, Martin, Monroe, Ohio, Orange, Owen, Perry, Pike, Posey, Ripley, Scott, Spencer, Switzerland, Vanderburgh, Warrick, Washington

What To Do If Your County Is Zone 1

1. Test your home. Buy a short-term radon test kit at any hardware store ($15–30), or hire a licensed radon tester for a certified measurement.
2. If results exceed 4 pCi/L, hire a licensed Indiana radon mitigator to install a mitigation system.
3. If results are 2–4 pCi/L, consider mitigation or retest with a long-term kit for a more accurate measurement.

The EPA recommends testing all homes, regardless of zone — even Zone 2 homes regularly test above 4 pCi/L.

The Only Way to Know: Test Your Home

County zone designations are averages. Your neighbor’s radon level can differ dramatically from yours based on:

• Foundation type — basements accumulate more radon than slab foundations
• Soil conditions — even within a county, some soil types release more radon
• Home construction — cracks, gaps, and openings affect how much radon enters
• Ventilation — newer, tighter homes can accumulate more radon than older drafty ones

A $20 test kit from your hardware store gives you the only number that actually matters: the radon level in your specific home.