Fall River County, SD: EPA's radon zone, explained

EPA places Fall River 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. Fall River County sits at the 38th percentile nationally for radon potential — above 38 of every 100 rated counties.

How Fall River County compares

Fall River County, South Dakota is home to about 7,359 people across 1,739.889 square miles. Averaged across its land area, Fall River County runs about 4 people per square mile. By population, Fall River County is the 890th largest of every county sharing its EPA zone — the 14th percentile by population within that zone. Geologically, Fall River County is grouped into EPA Region 8 alongside 290 other counties that share its rock and soil setting.

What this actually means for a house in Fall River County

Call it a middle case: above the 1.3 pCi/L most US homes average, below the 4 pCi/L line EPA uses to recommend mitigation — that's Fall River County's Zone 2 prediction. A Zone 2 rating is a moderate county-wide average, not a guarantee about any one house in Fall River County — testing is the only way to know an individual home's actual level.

If Fall River County tests above the action level

For a Fall River County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find South Dakota's state radon program

For Fall River County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Fall River County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.

Where Fall River County's figures come from

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. Whatever zone Fall River County carries, the zone explainer covers what it does and doesn't tell you about any one house.