What EPA's radon map says about Clark County

Clark County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Nationally, Clark County ranks higher in radon potential than 95% of rated counties (the 95th percentile).

Clark County by the numbers

About 127,479 people live in Clark County, Indiana, spread over 372.49 square miles. Averaged across its land area, Clark County runs about 342 people per square mile. Among counties sharing Clark County's EPA zone, it outranks 85% of them by population. Geologically, Clark County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.

Why the zone isn't the answer by itself

Clark County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. That doesn't mean every Clark County house tests high — a zone is a county-wide prediction, never a single-home reading — but it's a reason to test sooner rather than let it wait.

If Clark County tests above the action level

Mitigation cost doesn't depend on Clark County's zone — it depends on the house's foundation. A typical system runs $800–$2,500 (about $1,200 typical), and testing first is what tells you whether that's needed at all.

Find Indiana's state radon program

Clark County's test kit answers today; a Airthings radon monitor keeps answering for Clark County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.

More on how this number was built

The methodology guide shows exactly which EPA and Census sources feed Clark County's numbers. Whatever zone Clark County carries, the zone explainer covers what it does and doesn't tell you about any one house.