Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Carter County, Montana
EPA puts Carter County in Zone 1, its highest radon zone. Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Highest bordering
57.1%
Crook County
- Crook
- 57.1%
1 of 6 neighbours have 30+ tests, 2006 to 2015
Nearest county
47.3%
Dawson County, 122 miles
- Dawson
- 47.3%
- Montana
- 47.4%
Share at 4+ pCi/L, 55 tests, 2006 to 2015
Ground above low
100.0%
Level with Montana
- Carter
- 100.0%
- Montana
- 100.0%
Share of land USGS rates moderate or high potential
Tests reported
0
None published
A home here needs its own test
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Read a result for Carter County
Starts at EPA's action level
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 4.0 pCi/L
At or above 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher.
The data
Carter County, At a glance
Carter County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Carter County in
USGS geologic potential: Moderate across 76% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
No CDC test figures here
CDC has published no radon test figures for Carter County. Crook County, WY, the one bordering county with a figure over the 2006 to 2015 laboratory totals, reported 57.1% of its tests at or above 4 pCi/L.
Carter County, Compared
Carter County radon figures, compared
Calculated by Radon411Carter County has no radon test figure of its own from CDC, whose counts over the 2006 to 2015 laboratory totals name 52 other Montana counties and leave it out. Pooled across 52 Montana counties, 47.4% of reported tests reached that level; across every county in the country with a figure, 36.3%.
Crook County, WY, the one bordering county with a figure over the 2006 to 2015 laboratory totals, reported 57.1% of its tests at or above 4 pCi/L. Farther out, Dawson County (122 miles away) at 47.3%, Richland County (157 miles away) at 75.0% and Yellowstone County (183 miles away) at 43.1% have figures too. Statewide for the same period, Sheridan County reported the highest share (75.7%) and Hill County the lowest (35.0%).
EPA's 1993 map puts Carter County in Zone 1, the map's highest label: a predicted county average above 4 pCi/L. USGS geology rates 76% of the county's land moderate radon potential.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Carter County, Geology
The ground under Carter County
PredictedMost of the ground under Carter County is one class on USGS's geologic map: 76.1% of its land is moderate radon potential, with 23.9% high. The map puts 76.1% of Carter County in the area it calls Eastern Great Plains and 23.0% in Great Plains, with one smaller area beside them. USGS gives the first a radon index of 11, in the moderate band (9 to 11), and the second 12, in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Eastern Great Plains | Cretaceous marine shale and marine and nearshore sandstone, siltstone. | Moderate | 11 | 76.1% |
| Great Plains | Tertiary sandstone, siltstone, shale, coal. | High | 12 | 23.0% |
| Black Hills | Late Paleozoic sedimentary or Precambrian intrusive igneous rocks. | High | 12 | 0.8% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Carter County beside the ground around it
Montana as a whole has more high-potential ground than Carter County: 78.5% of its land, against 23.9% here. Of the 6 counties that border it, 5 have more high-potential ground, Custer County the most at 95.0%.
The map rates the ground, not the air in any home.
Local help
Carter County, Local resources
Radon testing and mitigation in Carter County
- Radon Control ProgramRadon Control Program, run by Montana DEQ, does not license radon professionals and offers free or discounted test kits, and answers questions about testing and mitigation in Montana.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Energy Bureau staff manage the radon information toll-free hotline and distribute subsidized radon test kits to Montana residents.
- Compare kits
- See the Montana directoryNo professionals are listed in Montana yet. The state program can point you to registered testers and mitigators.
What Montana's program says
- Phone
- 1-800-546-0483
- Licensing of radon professionals
Montana DEQ does not certify or require proof of certification for the contractors listed.
What it means
Carter County, Questions
Questions about radon in Carter County
Are radon levels high in Carter County?
No CDC testing statistics are published here for Carter County, Montana yet. Crook County, WY, the one bordering county with a figure over the 2006 to 2015 laboratory totals, reported 57.1% of its tests at or above 4 pCi/L.
Which counties border Carter County?
Carter County borders 6 counties: Harding County, SD, Fallon County, MT, Powder River County, MT, Crook County, WY, Butte County, SD and Custer County, MT.
Products
Carter County, Products
Testing a home in Carter County
No CDC figure names Carter County; the nearest county with one, Dawson County (122 miles away), reported 47.3% of its tests at or above 4 pCi/L over the 2006 to 2015 laboratory totals, the only reading nearby until a test of this home. In Zone 1 the year-round level in Carter County is the one to know: a long-term test (more than 90 days) or a monitor, with a short-term kit for a first answer.
Test kits and monitors3
See every kit and monitor
MonitorX-Sense
XR0A-iR Wi-Fi battery radon detector with a screen
- C-NRPP 2024/25: Not included
- Battery
- Wi-Fi
- Screen, app
Method: Alpha spectrometry
First reading: Within 24 hours
Short-term kitKidde
442020 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 3 days
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Carter County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Carter County
Explore
Carter County, Bordering counties
Counties bordering Carter County
Calculated by Radon411- Radon levels in Harding County, SDEPA zone 2
100.0%at or above 4 pCi/L
Median 7.9 pCi/L · 2 tests
- Radon levels in Fallon County, MTEPA zone 1
71.4%at or above 4 pCi/L
Median 5.2 pCi/L · 7 tests
- Radon levels in Powder River County, MTEPA zone 1
71.4%at or above 4 pCi/L
Median 4.5 pCi/L · 7 tests
- Radon levels in Crook County, WYEPA zone 1
57.1%at or above 4 pCi/L
Median 4.4 pCi/L · 42 tests
- Radon levels in Butte County, SDEPA zone 2
45.8%at or above 4 pCi/L
Median 3.3 pCi/L · 24 tests
- Radon levels in Custer County, MTEPA zone 1
37.9%at or above 4 pCi/L
Median 3.4 pCi/L · 29 tests
Carter County, Cities and towns
Cities and towns in Carter County
About 1,383 people live in Carter County by the Census Bureau's estimate for July 1, 2025, 23 fewer than in 2020 (−1.6%). Spread over its land, that is 0.4 people to the square mile. Ekalaka, its one incorporated place, has 398 residents, 28.8% of the total. CDC publishes no radon test count for Carter County; across Montana its counts for 2006 to 2015 come to 7.5 tests for every 1,000 residents (2025 estimate).
Ekalaka is the one incorporated place here; CDC publishes no figure by town, so it reads Carter County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Ekalaka | 398 | −0.3% | 28.8% |
One incorporated place, as listed in the U.S. Census Bureau’s 2020 place reference files. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025).
Carter County, Homes
Homes in Carter County
Of Carter County's 799 homes, 71% are detached houses, against 69% across Montana; 25% are mobile homes. Half of its homes were built before 1973, close to Montana's 1980: 39% date from before 1960 and 25% from 2000 or later. 62% of occupied homes are lived in by their owner (Montana: 69%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Carter County | Montana |
|---|---|---|
| Housing units | 799 | 522,939 |
| Detached houses | 71% | 69% |
| In buildings of 5 or more | 3% | 9% |
| Mobile homes | 25% | 10% |
| Built before 1960 | 39% | 26% |
| Built since 2000 | 25% | 27% |
| Middle year built | 1973 | 1980 |
| Owner-occupied | 62% | 69% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.