South Dakota Cities Ranked by Indoor Radon Levels
Measured averages from Airthings devices across South Dakota, USA. Action level: 4 pCi/L — the threshold at which remediation is recommended.
Box Elder has the highest measured indoor radon in South Dakota at 9.1 pCi/L, based on Airthings measurements across 22 cities.
Updated August 16, 2026
Highest city
9.1pCi/L
Box Elder
South Dakota city average
5.3pCi/L
across 22 cities
Above action level
15/ 22
cities
| # | Location | Avg level | Monitors | vs action level |
|---|---|---|---|---|
| 1 | Box Elder | 9.1 pCi/L | 9 | 2.3× over |
| 2 | Sturgis | 9.1 pCi/L | 6 | 2.3× over |
| 3 | Custer | 8.6 pCi/L | 17 | 2.1× over |
| 4 | Elk Point | 8.0 pCi/L | 6 | 2.0× over |
| 5 | Hot Springs | 6.5 pCi/L | 12 | 1.6× over |
| 6 | Mitchell | 6.5 pCi/L | 17 | 1.6× over |
| 7 | Spearfish | 6.3 pCi/L | 8 | 1.6× over |
| 8 | Brandon | 5.8 pCi/L | 15 | 1.5× over |
| 9 | Rapid City | 5.0 pCi/L | 35 | 1.3× over |
| 10 | Watertown | 4.8 pCi/L | 26 | 1.2× over |
| 11 | Rapid Valley | 4.7 pCi/L | 10 | 1.2× over |
| 12 | Salem | 4.7 pCi/L | 6 | 1.2× over |
| 13 | Pierre | 4.7 pCi/L | 18 | 1.2× over |
| 14 | Sioux Falls | 4.2 pCi/L | 90 | 1.1× over |
| 15 | North Sioux City | 4.2 pCi/L | 14 | 1.0× over |
| ✓ Below EPA action level (4 pCi/L) | ||||
| 16 | Harrisburg | 3.8 pCi/L | 25 | 1.0× under |
| 17 | Aberdeen | 3.7 pCi/L | 21 | 0.9× under |
| 18 | Brookings | 3.6 pCi/L | 17 | 0.9× under |
| 19 | Yankton | 3.4 pCi/L | 17 | 0.8× under |
| 20 | Tea | 3.4 pCi/L | 26 | 0.8× under |
| 21 | Colonial Pine Hills | 3.3 pCi/L | 24 | 0.8× under |
| 22 | Milbank | 3.0 pCi/L | 7 | 0.8× under |