Radon Levels in Willmar and Kandiyohi County
Minnesota is one of the highest radon states in the nation, and west-central Minnesota's glacial geology is a big part of why. Here is what the data says and what it means for your house.
The numbers
| Measure | Value | Source |
|---|---|---|
| Minnesota homes above the 4.0 pCi/L action level | About 2 in 5 | MDH, January 2024 |
| Minnesota average indoor radon | ~4.0 pCi/L | MDH |
| U.S. average indoor radon | ~1.3 pCi/L | EPA |
| Minnesota counties in EPA Zone 1 (highest potential) | 68 of 87 | EPA state map |
| U.S. lung cancer deaths from radon per year | ~21,000 | EPA / Surgeon General |
| U.S. homes above the action level | About 1 in 15 | EPA |
The Minnesota Department of Health publishes county-by-county test results on its interactive radon map. County averages describe the area, not your house: two identical homes on the same Willmar block can test wildly differently. The only number that matters for your family is the one from your own test.
Why this area tests high
Kandiyohi County sits on glacial till and old glacial lake sediment, mapped in detail in the Minnesota Geological Survey's county atlas. Those soils carry trace uranium, and uranium's decay chain produces radon gas. The gas moves easily through our loose, well-drained tills and finds any pressure path into a building: sump baskets, slab cracks, utility penetrations, crawl space floors.
Climate finishes the job. A Willmar home spends most of October through April closed up and heated. Warm air rising out of the house pulls replacement air up from the soil, a stack effect that turns the whole building into a gentle vacuum on the ground beneath it. That is why Minnesota's indoor average runs about three times the national average, and why winter tests read higher.
What this means for Willmar homes specifically
Willmar's median home was built in 1978. Minnesota did not require radon-resistant construction until June 2009, so the large majority of housing in Willmar, Spicer, New London, Atwater, and the surrounding townships was built with no radon protection. Sump baskets are common here, basements are usually finished and lived in, and both raise exposure: the sump is an open soil-gas path, and a finished basement means someone breathes that air for hours a day.
The practical takeaway is short. Test the house. If it reads 4.0 pCi/L or higher, fix it; the EPA also suggests considering a fix from 2.0 up. Costs and what drives them are in the Willmar cost guide.