Short-term kitFirst Alert
RD1 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 2 to 4 days
Locations and reports
Radon Levels in Sweet Grass County, Montana
EPA puts Sweet Grass County in Zone 2, its middle radon zone, and only 9 radon tests from it are on file with CDC (2008 to 2017, laboratory totals). Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Highest bordering
61.8%
Stillwater County
- Stillwater
- 61.8%
- Park
- 57.9%
2 of 5 neighbours have 30+ tests, 2006 to 2015
Nearest county
61.8%
Stillwater County, 28 miles
- Stillwater
- 61.8%
- Montana
- 47.4%
Share at 4+ pCi/L, 55 tests, 2006 to 2015
Ground above low
100.0%
Level with Montana
- Sweet Grass
- 100.0%
- Montana
- 100.0%
Share of land USGS rates moderate or high potential
Tests reported
10
Too few for a share
- Sweet Grass
- 10
- Needed
- 30
2006 to 2015, laboratory
EPA radon zone
Zone 2
Moderate potential
- 1
- Zone 2
- 3
1 highest, 3 lowest
EPA predicts 2 to 4 pCi/L indoors
Read a result for Sweet Grass 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
Sweet Grass County, At a glance
Sweet Grass County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Sweet Grass County is a
USGS geologic potential: Moderate across 99% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Sweet Grass County, 2008 to 2017, laboratory
CDC holds 9 reported tests for Sweet Grass County over the 2008 to 2017 laboratory totals, with a median of 11.9 pCi/L: too few to describe a county (Radon411 reads a share from 30 tests up). Sweet Grass County beside the counties around it is how this page reads it.
What these figures count
Only 9 tests were reported to CDC for Sweet Grass County over 2008 to 2017 (laboratory totals), and tests are often run on homes being sold or already suspected of a problem: so few describe neither the county nor this house.
Measured: CDC tracking data. Figure above: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).
Sweet Grass County, Compared
Sweet Grass County radon figures, compared
Calculated by Radon411CDC's largest figure for Sweet Grass County rests on 10 tests over the 2006 to 2015 laboratory totals, 8 of them at or above 4 pCi/L, so each test moves its share by 10.0 points and no rank or comparison is drawn from it. Results reached as high as 35.4 pCi/L, with a middle value of 9.7 pCi/L.
Of the counties bordering it, 2 have a figure over the 2006 to 2015 laboratory totals: Stillwater County reported the largest share at or above 4 pCi/L, 61.8%, and Park County the smallest, 57.9%. Farther out, Carbon County (60 miles away) at 52.5%, Gallatin County (62 miles away) at 48.8% and Yellowstone County (81 miles away) at 43.1% have figures too. Pooled across 52 Montana counties, 47.4% of reported tests reached that level; across every county in the country with a figure, 36.3%.
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 Sweet Grass County in Zone 2, its middle label: a predicted county average between 2 and 4 pCi/L. USGS geology rates 99% of the county's land moderate radon potential.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Sweet Grass County, Geology
The ground under Sweet Grass County
PredictedMost of the ground under Sweet Grass County is one class on USGS's geologic map: 99.2% of its land is moderate radon potential, with 0.8% high. The map puts 83.8% of Sweet Grass County in the area it calls Plains and Mountains and 15.3% in Absaroka Volcanic Field, with one smaller area beside them. USGS gives both a radon index of 10, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Plains and Mountains | Marine and continental shale, siltstone, and sandstone of Cretaceous and Tertiary ages, and volcanic rocks. | Moderate | 10 | 83.8% |
| Absaroka Volcanic Field | Intrusive and extrusive volcanic rocks and overlying sediments. | Moderate | 10 | 15.3% |
| Northern Rocky Mountains | Granitic, metaigneous, metasedimentary rocks, valley fill colluvium and alluvium. | High | 13 | 0.8% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Sweet Grass County beside the ground around it
Montana as a whole has more high-potential ground than Sweet Grass County: 78.5% of its land, against 0.8% here. Of the 5 counties that border it, 3 have more high-potential ground, Meagher County the most at 78.3%.
The map rates the ground, not the air in any home.
Local help
Sweet Grass County, Local resources
Radon testing and mitigation in Sweet Grass 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
Sweet Grass County, Questions
Questions about radon in Sweet Grass County
Are radon levels high in Sweet Grass County?
Over the 2008 to 2017 laboratory totals, 88.9% of the radon tests reported to CDC for Sweet Grass County, Montana were at or above 4 pCi/L, and the median reported pre-mitigation result was 11.9 pCi/L. Of the counties bordering it, 2 have a figure over the 2006 to 2015 laboratory totals: Stillwater County reported the largest share at or above 4 pCi/L, 61.8%, and Park County the smallest, 57.9%.
Which counties border Sweet Grass County?
Sweet Grass County borders 5 counties: Park County, Stillwater County, Wheatland County, Golden Valley County and Meagher County.
Products
Sweet Grass County, Products
Testing a home in Sweet Grass County
No CDC figure names Sweet Grass County; the nearest county with one, Stillwater County (28 miles away), reported 61.8% 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 2 a short-term kit (2 to 90 days) is the quick first check in Sweet Grass County; a long-term test tells the year-round average.
Test kits and monitors3
See every kit and monitor
Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
MonitorPYZYCKYH
RD17 plug-in radon detector with a rechargeable battery and color screen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
First reading: Within 6 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Sweet Grass County, Bordering counties
Counties bordering Sweet Grass County
Calculated by Radon411- Radon levels in Golden Valley CountyEPA zone 2
100.0%at or above 4 pCi/L
Median 5.0 pCi/L · 1 test
- Radon levels in Stillwater CountyEPA zone 1
61.8%at or above 4 pCi/L
Median 5.0 pCi/L · 55 tests
- Radon levels in Park CountyEPA zone 1
57.9%at or above 4 pCi/L
Median 5.1 pCi/L · 140 tests
- Radon levels in Wheatland CountyEPA zone 2
50.0%at or above 4 pCi/L
Median 5.5 pCi/L · 2 tests
- Radon levels in Meagher CountyEPA zone 1
0.0%at or above 4 pCi/L
Median 3.6 pCi/L · 1 test
Sweet Grass County, Cities and towns
Cities and towns in Sweet Grass County
The Census Bureau estimates 3,762 residents in Sweet Grass County for July 1, 2025, 88 more than in 2020 (+2.4%). Spread over its land, that is 2.0 people to the square mile. Big Timber, its one incorporated place, has 1,686 residents, 44.8% of the total. Reported testing is thin here: 10 tests over 2006 to 2015, or 2.7 for every 1,000 residents (2025 estimate), where Montana as a whole comes to 7.5.
Big Timber is the one incorporated place here; CDC publishes no figure by town, so it reads Sweet Grass County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Big Timber | 1,686 | +2.7% | 44.8% |
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).
Sweet Grass County, Homes
Homes in Sweet Grass County
Sweet Grass County is a place of houses on their own lots: 78% of its 1,929 homes are detached single-family houses, against 69% across Montana. Half of its homes were built before 1979, close to Montana's 1980: 31% date from before 1960 and 19% from 2000 or later. Owners live in 76% of the occupied homes (Montana: 69%), so for most households a test and a fix are their own to order.
| Homes | Sweet Grass County | Montana |
|---|---|---|
| Housing units | 1,929 | 522,939 |
| Detached houses | 78% | 69% |
| In buildings of 5 or more | 2% | 9% |
| Mobile homes | 11% | 10% |
| Built before 1960 | 31% | 26% |
| Built since 2000 | 19% | 27% |
| Middle year built | 1979 | 1980 |
| Owner-occupied | 76% | 69% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.