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Combined exposures · In-home geology

Radon and arsenic in Illinois homes

Two in-home geologic exposures, estimated for the same Illinois ZIP codes: modeled indoor radon and modeled groundwater arsenic. This page is scoped to Illinois.

IllinoisData release 2026Modeled inputs

Across parts of Illinois, two separate geologic exposures show up in the same ZIP codes — a modeled likelihood of elevated arsenic in groundwater, and modeled indoor radon. Here is exactly what each measurement is, and the federal reference each is measured against.

How we measure this →
Modeled indoor radonEPA action levelModeled · ZCTA-native

Where the modeled value crosses the line, this area's modeled radon runs above EPA's 4 pCi/L action level — the level at which the EPA recommends taking action to reduce indoor radon. It is an action level, a recommendation to act, never a regulatory limit.

EPA indoor-radon action level — 4 pCi/L. A recommendation to act, not a regulatory limit.

Modeled groundwater arsenicEPA public-water limitModeled likelihood

USGS models a high likelihood that groundwater arsenic here exceeds 10 µg/L — the level EPA sets as the limit for public water systems. Most private wells are federally unregulated, so this is a modeled likelihood, never a measured exceedance.

EPA drinking-water maximum contaminant limit — 10 µg/L. Applies to public systems; private wells are not covered.

What this is — and isn't. These are two exposures estimated for the same place. This page does not claim one causes the other, does not combine them into a single risk number, and does not link either to any health outcome. It reports where both figures are elevated together, and nothing more.

Illinois ZIP codes where both are elevated

The Illinois ZIP codes (ZCTAs) that rank among the highest 10% of US ZIP codes for both modeled exposures. The ranking is national; this list is Illinois only. How each area reads depends on whether its modeled radon actually crosses the 4 pCi/L action level — see the two labels below.

Above action levelmodeled radon crosses 4 pCi/L — the federal-reference sentence rendersElevated (top 10% in the US)in the top 10% of US ZIP codes but below 4 pCi/L — reads as a ranking, not the 4 pCi/L sentence
  • 61721in ArmingtonElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 62612in AshlandElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61723in AtlantaElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61813in BementElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61420in BlandinsvilleElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 62513in Blue MoundElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61421in BradfordElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61523in ChillicotheElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 62326in ColchesterElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61733in Deer CreekElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61734in DelavanElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 62634in ElkhartElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61530in EurekaElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61438in Good HopeElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 62642in GreenviewElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 62643in HartsburgElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61747in HopedaleElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61565in HopewellElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 62539in IlliopolisElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 62650in JacksonvilleElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61330in La MoilleElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61752in Le RoyElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 62656in LincolnElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61759in MinierElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61550in MortonElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 62548in Mount PulaskiElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 62550in MoweaquaElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61349in OhioElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 62677in Pleasant PlainsElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61559in PrincevilleElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61770in SaybrookElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61774in StanfordElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61369in TolucaElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61483in ToulonElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61776in TowandaElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61568in TremontElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61777in WapellaElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

  • 61491in WyomingElevated (top 10% in the US)

    This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

Coverage & how to read this

Modeled, not measured. Indoor radon uses the Li national ZCTA-level model; groundwater arsenic uses the USGS private-well probability model. Neither is a reading from your home or tap. A ZIP with an unobservable leg is shown as not measured, never as "not impacted." Both references are federal: radon's 4 pCi/L is an action level (a recommendation to act), arsenic's 10 µg/L is the maximum contaminant limit EPA sets for public water systems. A ZIP reaches this list by ranking among the highest 10% of US ZIP codes for each exposure — the ranking is national, and this list is Illinois only. Read the full combined-exposure methodology →

Each ZIP links to its full ZipVitals page. Illinois only — the national list is on the explainer page.