Is Johnson County, IN a radon risk area?
EPA's own radon map rates Johnson County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally, Johnson County ranks higher in radon potential than 96% of rated counties (the 96th percentile).
Johnson County by the numbers
About 170,614 people live in Johnson County, Indiana, spread over 320.415 square miles. Averaged across its land area, Johnson County runs about 532 people per square mile. Rank 112 by population within its EPA zone puts Johnson County at the 90th percentile among zone peers. Johnson County falls in EPA Radon Region 5, one of 524 counties nationally EPA assigns to that same geologic province.
Why the zone isn't the answer by itself
Johnson County carries a Zone 1 label because its predicted average clears 4 pCi/L outright — three-plus times the 0.4 pCi/L typical outdoors and above the 1.3 pCi/L most homes see. A Zone 1 rating means testing is worth doing sooner rather than later, but it is still county-wide average, not a reading for any single house — some homes in Johnson County will test well under the action level, and EPA's guidance is to test regardless of zone.
If Johnson County tests above the action level
Nothing about Johnson County's EPA zone changes the mitigation number: $800–$2,500 nationally (around $1,200 typical), set by the house's foundation rather than the county it sits in — and only relevant once a test actually clears 4 pCi/L.
Find Indiana's state radon program
Johnson County's test kit answers today; a Airthings radon monitor keeps answering for Johnson County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. Use code RADONZONE-10OFF at checkout for 10% off.
More on how this number was built
Johnson County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Johnson County carries, the zone explainer covers what it does and doesn't tell you about any one house.