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Radon Levels in Grant County, Indiana

EPA puts Grant County in Zone 1, its highest radon zone, and high results are common there: 58.2% of the 79 radon tests reported to CDC (2008 to 2017, laboratory totals) came back at or above 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    58.2%

    19.3 pts above IN

    Grant
    58.2%
    Indiana
    38.9%

    79 tests, 2008 to 2017

  • Median result

    4.6pCi/L

    Action level reached

    Grant
    4.6 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    79

    52nd of 69 by tests

    Grant
    79
    St. Joseph
    7,346

    Reported to CDC before any fix, 2008 to 2017

  • EPA radon zone

    Zone 1

    Highest potential

    1. Zone 1
    2. 2
    3. 3

    1 highest, 3 lowest

    EPA predicts over 4 pCi/L indoors

  • Rank in Indiana

    6 of 69

    Top quarter

    Grant
    58.2%
    Miami
    63.3%

    By share, of 69 with 30+ tests

Read a result for Grant County

Starts at Grant County's median, 4.6 pCi/L

4.6pCi/L

EPA’s own thresholds; the figures are the area’s, never this home’s.

EPA’s reading of 4.6 pCi/L

At or above 4 pCi/L

  1. Under 20 to 1.9 pCi/L
  2. 2 to 4consider a fix
  3. 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. Grant County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Grant County, At a glance

Grant County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Grant County in and predicts an average indoor of greater than 4 pCi/L (greater than 150 Bq/m³) across the county. That is one forecast for the whole county, not a reading of any address in it; homes above EPA's turn up in all three zones.

USGS geologic potential: High across 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Grant County, 2008 to 2017, laboratory

Reported results by concentration band, Grant County, 2008 to 2017, laboratory
Under 2 pCi/L: 20%2 to 4 pCi/L: 22%4 pCi/L and above: 58%

Of 79 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Grant County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L1620.3%
2 to 4 pCi/L1721.5%
4 pCi/L and above4658.2%
What these figures count

These are the 79 tests reported to CDC for Grant County over 2008 to 2017 (laboratory totals), many from homes being sold or already suspected of a problem: they describe the county's reported tests, not this house.

Measured: CDC tracking data. Figure above: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).

How to read these figures

Grant County, Compared

Grant County radon figures, compared

Calculated by Radon411

More than half: 58.2% of the 79 radon tests reported to CDC for Grant County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 6th of 69 Indiana counties with 30 or more tests for the same period. That is 19.3 points above the 38.9% pooled from 92 Indiana counties.

The median result, 4.6 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 31.2 pCi/L. The rest split 20.3% under 2 pCi/L and 21.5% from 2 to 4 (Indiana: 32.8% and 28.3%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 58.2% share point the same way here.

2 of its 8 bordering counties with figures ran higher, led by Miami County at 63.3%; Huntington County reported 43.8%. Statewide for the same period, Miami County reported the highest share (63.3%) and Jasper County the lowest (14.1%).

CDC's ten-year totals for Grant County went from 69 tests (2005 to 2014) to 79 (2008 to 2017), the share going from 65.2% to 58.2%.

Nationally, every county with a figure for the same period pools to 35.7%; Grant County sits 22.5 points above it. CDC also counts 6 tests taken after mitigation in Grant County for the same period: tests in homes where a fix was already in.

Grant County against Indiana, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Grant County
Grant County7958.2%4.6 pCi/LThis county
Indiana, pooled92 counties, pooled43,14838.9%Not pooled−19.3 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−22.5 points
Harrison Countyhighest in the state22162.4%5.5 pCi/L+4.2 points
Jasper Countylowest in the state7114.1%1.2 pCi/L−44.1 points
Miami County, INborders it3063.3%5.3 pCi/L+5.1 points
Wabash County, INborders it9159.3%5.8 pCi/L+1.1 points
Delaware County, INborders it18755.1%4.2 pCi/L−3.1 points
Tipton County, INborders it6949.3%3.9 pCi/L−8.9 points
Howard County, INborders it21649.1%3.8 pCi/L−9.1 points
Madison County, INborders it23949.0%3.8 pCi/L−9.2 points
Wells County, INborders it16147.8%3.6 pCi/L−10.4 points
Huntington County, INborders it16943.8%3.5 pCi/L−14.4 points
Blackford County, INborders it1136.4%3.6 pCi/L−21.8 points
Where Grant County's reported results fell, 2008 to 2017, laboratory, beside Indiana and the United States
ResultGrant County testsGrant County shareIndiana shareU.S. shareAgainst Indiana
Under 2 pCi/L1620.3%32.8%39.6%−12.5 points
2 to 4 pCi/L1721.5%28.3%24.7%−6.8 points
4 pCi/L and above4658.2%38.9%35.7%+19.3 points
Grant County ranked among the 69 Indiana counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Miami County1 of 693063.3%5.3 pCi/L
Harrison County2 of 6922162.4%5.5 pCi/L
Benton County3 of 693461.8%5.7 pCi/L
Carroll County4 of 693860.5%5.8 pCi/L
Wabash County5 of 699159.3%5.8 pCi/L
Grant County6 of 697958.2%4.6 pCi/L
LaPorte County7 of 6979258.2%5.0 pCi/L
DeKalb County8 of 6924256.6%4.4 pCi/L
Wayne County9 of 6914056.4%4.5 pCi/L
Steuben County10 of 6914055.7%4.5 pCi/L
Delaware County11 of 6918755.1%4.2 pCi/L
Grant County ten-year laboratory totals, against Indiana's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIndiana, pooledChange from the row before
2008 to 20177958.2%4.6 pCi/L31.2 pCi/L38.9%+0.2 points
2007 to 20166958.0%5.3 pCi/L31.2 pCi/L39.2%−4.9 points
2006 to 20157062.9%5.8 pCi/L31.2 pCi/L39.6%−2.3 points
2005 to 20146965.2%6.0 pCi/L31.2 pCi/L39.3%First on file

Pooled shares: Radon411's sum of CDC's county counts for one period.

Grant County, Geology

The ground under Grant County

Predicted

USGS's geologic map puts all of Grant County's mapped land in one class: high radon potential. All of it lies in the area the map calls Huron-Erie Lobe, to which USGS gives a radon index of 13, in the high band (12 to 17).

USGS's geologic areas under Grant County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Huron-Erie LobeCalcareous clayey and loamy glacial deposits derived from marine carbonate and clastic sedimentary rocks.High13100%

Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.

Grant County beside the ground around it

Grant County has more high-potential ground than Indiana as a whole: 100% of its land against 56.6%. Of the 9 counties that border it, none has as large a share of high-potential ground; Blackford County comes nearest at 100%.

Share of land by USGS radon potential: Grant County, the 9 counties bordering it and Indiana
AreaEPA zoneLow potentialModerate potentialHigh potential
Grant CountyZone 1NoneNone100%
Blackford CountyZone 1NoneNone100%
Huntington CountyZone 1NoneNone100%
Madison CountyZone 1NoneNone100%
Delaware CountyZone 1NoneNone100%
Howard CountyZone 1NoneNone100%
Wabash CountyZone 1NoneNone100%
Tipton CountyZone 1NoneNone100%
Miami CountyZone 1NoneNone100%
Wells CountyZone 1NoneNone100%
Indiana92 counties, pooled by land areaVariesNone43.4%56.6%

The map rates the ground, not the air in any home.

Local help

Grant County, Local resources

Radon testing and mitigation in Grant County

What Indiana's program says
Phone
1-800-272-9723
Licensing of radon professionals
According to the Indiana Radon Rule, 410 IAC 5.1, everyone who is serving Indiana by doing radon testing, analysis and mitigation (radon reduction) in residential structures must be certified by the Indiana State Department of Health.

What it means

Grant County, Questions

Questions about radon in Grant County

Are radon levels high in Grant County?

Over the 2008 to 2017 laboratory totals, 58.2% of the radon tests reported to CDC for Grant County, Indiana were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.6 pCi/L. Of 69 Indiana counties with 30 or more tests for the same period, 5 reported a higher share; pooled, the state comes to 38.9%.

Which counties border Grant County?

Grant County borders 9 counties: Blackford County, Huntington County, Madison County, Delaware County, Howard County, Wabash County, Tipton County, Miami County and Wells County.

Products

Grant County, Products

Testing a home in Grant County

In Grant County, 58.2% of 79 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 38.9% pooled across Indiana. In Zone 1 the year-round level in Grant 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

Grant County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Grant County

Explore

Grant County, Bordering counties

Counties bordering Grant County

Calculated by Radon411

Grant County, Cities and towns

Cities and towns in Grant County

Grant County's population has barely moved since 2020: 66,524 residents on July 1, 2025 against 66,505 then, by the Census Bureau's estimates. That works out to 161 people per square mile of land. Its largest town, Marion, has 28,234 residents, 42.4% of the total. Reported testing is thin here: 79 tests over 2008 to 2017, or 1.2 for every 1,000 residents (2025 estimate), where Indiana as a whole comes to 6.2.

From Marion to Fowlerton, CDC publishes no figure by town: each reads Grant County's.

The cities and towns in Grant County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Marion28,234Level42.4%
Gas City6,081−1.0%9.1%
Upland3,835+0.3%5.8%
Fairmount2,670−0.2%4.0%
Jonesboro1,510+0.1%2.3%
Converseextends beyond Grant County1,128−2.3%Counted whole
Sweetser1,069+0.2%1.6%
Swayzee904−1.0%1.4%
Van Buren775−0.3%1.2%
Matthews484+0.8%0.7%
Fowlerton271+1.1%0.4%

11 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). A place that extends beyond Grant County is counted whole, so it has no share.

Grant County, Homes

Homes in Grant County

Grant County is a place of houses on their own lots: 80% of its 29,878 homes are detached single-family houses, against 73% across Indiana. The homes are older than Indiana's as a whole: half were built before 1963 (1976 for Indiana), and 46% date from before 1960. 72% of occupied homes are lived in by their owner (Indiana: 70%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Grant County, Indiana, 2019 to 2023
HomesGrant CountyIndiana
Housing units29,8782,953,344
Detached houses80%73%
In buildings of 5 or more6%13%
Mobile homes6%4%
Built before 196046%32%
Built since 20009%21%
Middle year built19631976
Owner-occupied72%70%

Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.