Is Marion County, MO a radon risk area?

EPA places Marion County in Zone 2 - Moderate Potential — a predicted county-wide average indoor radon level between 2 and 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Nationally that's the 50th percentile for radon potential — Marion County outranks 50% of every county EPA has rated.

Marion County by the numbers

About 28,425 people live in Marion County, Missouri, spread over 436.931 square miles. Averaged across its land area, Marion County runs about 65 people per square mile. Rank 501 by population within its EPA zone puts Marion County at the 52nd percentile among zone peers. Geologically, Marion County is grouped into EPA Region 7 alongside 411 other counties that share its rock and soil setting.

Zone vs. an actual test

Neither at the 4 pCi/L action level nor down at the roughly 1.3 pCi/L national indoor norm, Marion County's Zone 2 prediction lands in the gap between the two. Middle-of-the-pack doesn't mean risk-free for any one Marion County address — a moderate county average still leaves individual homes to test either side of it.

If Marion County tests above the action level

Nothing about Marion 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 Missouri's state radon program

Marion County's test kit answers today; a Airthings radon monitor keeps answering for Marion 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

Marion County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Marion County carries, the zone explainer covers what it does and doesn't tell you about any one house.