Short-term kit
RA400 short-term liquid scintillation radon test kit, lab fee included
- Lab fee included
Method: Liquid scintillation
In home: 48 to 96 hours
Locations and reports
Radon Levels in Mercer County, Missouri
EPA puts Mercer County in Zone 2, its middle radon zone, and only 1 radon test from it is on file with CDC (2020). Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Highest bordering
34.8%
Wayne County
- Wayne
- 34.8%
- Decatur
- 25.9%
2 of 6 neighbours have 30+ tests, 2008 to 2017
Nearest county
26.7%
Daviess County, 39 miles
- Daviess
- 26.7%
- Missouri
- 30.6%
Share at 4+ pCi/L, 30 tests, 2008 to 2017
Ground above low
100.0%
5.8 pts above Missouri
- Mercer
- 100.0%
- Missouri
- 94.2%
Share of land USGS rates moderate or high potential
Tests reported
11
Too few for a share
- Mercer
- 11
- Needed
- 30
2008 to 2017, 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 Mercer 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
Mercer County, At a glance
Mercer County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Mercer County is a
USGS geologic potential: Moderate across 100% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Mercer County, 2020
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 50.0% |
| 2015 | 0.0% |
| 2016 | 0.0% |
| 2017 | 100.0% |
| 2020 | 0.0% |
2020: 0.0%. Across these years the share ran from 0.0% to 100.0%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
Only 1 test was reported to CDC for Mercer County over 2020, 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: 2020. Measured data period: 2005 to 2020 (every CDC figure on file).
Mercer County, Compared
Mercer County radon figures, compared
Calculated by Radon411CDC's largest figure for Mercer County rests on 11 tests over the 2008 to 2017 laboratory totals, 3 of them at or above 4 pCi/L, so each test moves its share by 9.1 points and no rank or comparison is drawn from it. Results reached as high as 23.7 pCi/L, with a middle value of 1.7 pCi/L.
Of the counties bordering it, 2 have a figure over the 2008 to 2017 laboratory totals: Wayne County, IA reported the largest share at or above 4 pCi/L, 34.8%, and Decatur County, IA the smallest, 25.9%. Farther out, Daviess County (39 miles away) at 26.7%, Livingston County (44 miles away) at 22.4% and Linn County (45 miles away) at 18.9% have figures too. Pooled across 115 Missouri counties, 30.6% of reported tests reached that level; across every county in the country with a figure, 35.7%.
Statewide for the same period, Atchison County reported the highest share (69.9%) and Vernon County the lowest (8.8%). EPA's 1993 map puts Mercer County in Zone 2, its middle label: a predicted county average between 2 and 4 pCi/L. USGS geology rates 100% of the county's land moderate radon potential.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Mercer County, Geology
The ground under Mercer County
PredictedUSGS's geologic map puts all of Mercer County's mapped land in one class: moderate radon potential. All of it lies in the area the map calls Dissected Till Plains, to which USGS gives a radon index of 11, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Dissected Till Plains | Till-covered Pennsylvanian sandstone, shale, and limestone. | Moderate | 11 | 100% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Mercer County beside the ground around it
Across Missouri 8.2% of the land is rated high; none of Mercer County's is. Of the 6 counties that border it, 3 have more high-potential ground, Decatur County, IA the most at 91.4%.
The map rates the ground, not the air in any home.
Local help
Mercer County, Local resources
Radon testing and mitigation in Mercer County
- Missouri Radon ProgramMissouri Radon Program, run by Missouri Department of Health and Senior Services, offers free or discounted test kits, and answers questions about testing and mitigation in Missouri.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Free radon test kits are available for Missouri residents (limit one per household).
- Compare kits
- Professionals in Missouri27 professionals are listed in Missouri.
What Missouri's program says
- Phone
- 573-751-6102
- radon@health.mo.gov
What it means
Mercer County, Questions
Questions about radon in Mercer County
Are radon levels high in Mercer County?
In 2020, 0.0% of the radon tests reported to CDC for Mercer County, Missouri were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.9 pCi/L. Of the counties bordering it, 2 have a figure over the 2008 to 2017 laboratory totals: Wayne County, IA reported the largest share at or above 4 pCi/L, 34.8%, and Decatur County, IA the smallest, 25.9%.
Which counties border Mercer County?
Mercer County borders 6 counties: Harrison County, MO, Grundy County, MO, Decatur County, IA, Wayne County, IA, Putnam County, MO and Sullivan County, MO.
Products
Mercer County, Products
Testing a home in Mercer County
No CDC figure names Mercer County; the nearest county with one, Daviess County (39 miles away), reported 26.7% of its tests at or above 4 pCi/L over the 2008 to 2017 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 Mercer County; a long-term test tells the year-round average.
Test kits and monitors3
See every kit and monitor
Long-term kit
RL416 long-term radon test kit, lab fee included
- Lab fee included
Method: Alpha track
In home: 90 days to 12 months
Monitor
RadonPro Wi-Fi radon monitor with a built-in Geiger counter
- C-NRPP 2024/25: Not included
- Plug-in
- Wi-Fi
- Alarm
- Screen, app
First reading: Within 5 minutes
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Mercer County, Bordering counties
Counties bordering Mercer County
Calculated by Radon411- Radon levels in Grundy County, MOEPA zone 2
37.0%at or above 4 pCi/L
Median 2.8 pCi/L · 27 tests
- Radon levels in Wayne County, IAEPA zone 1
34.8%at or above 4 pCi/L
Median 3.0 pCi/L · 46 tests
- Radon levels in Putnam County, MOEPA zone 2
33.3%at or above 4 pCi/L
Median 1.8 pCi/L · 9 tests
- Radon levels in Sullivan County, MOEPA zone 2
33.3%at or above 4 pCi/L
Median 1.4 pCi/L · 6 tests
- Radon levels in Harrison County, MOEPA zone 2
29.2%at or above 4 pCi/L
Median 1.9 pCi/L · 24 tests
- Radon levels in Decatur County, IAEPA zone 1
25.9%at or above 4 pCi/L
Median 2.5 pCi/L · 85 tests
Mercer County, Cities and towns
Cities and towns in Mercer County
About 3,404 people live in Mercer County by the Census Bureau's estimate for July 1, 2025, 112 fewer than in 2020 (−3.2%). Spread over its land, that is 7.5 people to the square mile. Its largest town, Princeton, has 970 residents, 28.5% of the total. Together its 3 incorporated places hold 36.4% of those residents; the other 63.6% live outside any of them. Reported testing is thin here: 11 tests over 2008 to 2017, or 3.2 for every 1,000 residents (2025 estimate), where Missouri as a whole comes to 9.3.
From Princeton to South Lineville, CDC publishes no figure by town: each reads Mercer County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Princeton | 970 | −3.4% | 28.5% |
| Mercer | 254 | −3.1% | 7.5% |
| South Lineville | 14 | Level | 0.4% |
3 incorporated places, 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).
Mercer County, Homes
Homes in Mercer County
Mercer County is a place of houses on their own lots: 82% of its 1,908 homes are detached single-family houses, against 70% across Missouri. Half of its homes were built before 1971, close to Missouri's 1978: 34% date from before 1960 and 15% from 2000 or later. Owners live in 79% of the occupied homes (Missouri: 68%), so for most households a test and a fix are their own to order.
| Homes | Mercer County | Missouri |
|---|---|---|
| Housing units | 1,908 | 2,809,501 |
| Detached houses | 82% | 70% |
| In buildings of 5 or more | 5% | 13% |
| Mobile homes | 8% | 5% |
| Built before 1960 | 34% | 28% |
| Built since 2000 | 15% | 21% |
| Middle year built | 1971 | 1978 |
| Owner-occupied | 79% | 68% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.