Cook County, with Will and DuPage parcels. Illinois radon mitigation license RNM2018212

Radon mitigation in Lemont

Lemont is Cook County for about 95 percent of the village, with some parcels in Will and DuPage, so the kit follows the county on your tax bill. A Cook County address can request the free Cook County mail-in kit. A Will County parcel buys the $8 Will County kit at the health department office in Joliet, Bolingbrook, or Monee. For a DuPage parcel, text Bill the address and he will point you to a current kit. A reusable detector works in any of the three.

Text Bill the number and he’ll tell you what it means, free. If it comes back high, he comes out from Tinley Park, looks at the foundation and any builder pipe, and gives you the price. A bluff lot and a valley lot get the same visit.

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Three counties, two valleys

Lemont is not a flat Cook County suburb with one kind of ground under it. The village sits where two old outlets of a glacial lake come together, and the village limits cross three counties. That is why a Lemont address gets its own page.

Village community statistics list the county split as Cook for about 95 percent of Lemont, with the rest in DuPage and Will. The village tax page says the same thing in parcel language. Most parcels are Cook County. Some inside the village limits are Will or DuPage. The kit follows the county on the tax bill, not the word Lemont on the mailing address.

What licensed tests in Lemont show

On October 14, 2026 we counted valid licensed measurements in the radon layer IEMA publishes with its public map. The service description dates that pull to July 18, 2022. We kept records marked valid that have a numeric result. A home can show up more than once. IEMA says the public map keeps only the highest measurement per address, for 2003 through 2019, so these figures are not a reprint of the map totals. This cut is wider than the one on our other town pages, which leave out records with a mitigation system noted, so the county shares differ a little from page to page.

For records whose city name is Lemont, 543 of 1,354 valid tests were at or above 4.0 pCi/L. That is 40.1 percent. The same count landed on ZIP 60439. Across the whole layer, Cook County was 17,359 of 84,118, or 20.6 percent. DuPage County was 31,104 of 89,264, or 34.8 percent. Will County was 16,091 of 41,726, or 38.6 percent.

Those are measurements people chose to order, not a census of Lemont. The EPA June 2024 county file places Cook, DuPage, and Will in Zone 2. A zone is a county label. It does not assign a level to your foundation. Testing is how you get the number that belongs to the home.

The ground under Lemont

The Illinois State Geological Survey describes a Y-shaped Chicago Outlet Valley cut by glacial Lake Chicago. The north arm is the Des Plaines Valley, now the path of the Des Plaines River and the Chicago Sanitary and Ship Canal. The south arm is the Sag Valley, which holds the Calumet-Sag Channel and no large natural river. Along that valley floor, Silurian dolomite is exposed or buried only shallowly under glacial sediment.

Canal crews met that rock in Lemont. The Village of Lemont guide to the Heritage Quarries says the Illinois and Michigan Canal, begun in 1836 and finished in 1848, was especially hard to dig here because dolomite lay just under the topsoil. The quarries that followed supplied stone for buildings including the Chicago Water Tower. The Forest Preserves of Cook County still describe the Sag Quarries, near Lemont at 60439, as old limestone quarries that are now lakes.

A Geological Society of America abstract on Athens Marble puts the Lemont and Joliet quarries on the Illinois and Michigan Canal. The product was Silurian dolomite sold as building stone. The stone is the local bedrock. It is not a radon meter.

Radon-222 is the gas in the uranium-238 decay chain. It is born when radium-226 decays. The EPA public fact sheet gives radon a half-life of 3.8 days, long enough for the gas to move through pores in till or along an opening in dolomite, and short enough that it does not hang around for months. In cold weather, warm indoor air rises and leaves near the top of the home. Pressure at the foundation drops, and soil gas is pulled in. EPA has described that winter pull as the stack effect.

A bluff lot and a valley-floor lot can test far apart. Quarry history, the canal, and the dolomite explain the ground you can see. They do not predict your result.

Lemont homes, from the Census and the village

A June 2026 CMAP community snapshot for Lemont, drawn from the Census Bureau 2020 to 2024 survey, puts the median year built at 1995. About 14.9 percent of housing units were built in 2010 or later, and 48.1 percent were built from 1990 to 2009. Detached single-family homes are 75.4 percent of the units. Attached single-family homes are 15.0 percent. The Census Bureau July 1, 2025 population figure for the village is 18,513.

Illinois has required passive radon features in new one-family and two-family homes built after June 1, 2013. The Will County Health Department states that scope and that date. The 2010-or-later Census bin is the only Lemont group that can include those homes, and it also includes homes finished before the rule. A white pipe with no fan is a photo worth sending. It is not proof of anything until someone looks.

Trim-colored radon vent pipe and an exterior fan beside brick on a Lemont home

From our work

A Lemont exterior run

One Lemont install, with the fan outside and trim-colored pipe on the brick. The discharge ends about 12 inches past the gutter.

Nearby pages

Lemont pages along the valley and down the hill:

Lemont questions

Which county kit applies to a Lemont address?

The county on the tax bill. The village says about 95 percent of Lemont is Cook County, with some parcels in DuPage and Will. Suburban Cook addresses can request the free mailed kit from the Cook County Department of Public Health. Will County parcels can buy the $8 kit at the Joliet, Bolingbrook, or Monee office. For a DuPage parcel, text Bill the address and he will point you to a current kit.

Do the Lemont quarries or the canal mean my home will test high?

No. The quarries and the Illinois and Michigan Canal explain why dolomite is close to the surface in the valley. Radon comes from uranium already in soil and rock, and it moves differently through till than through fractured dolomite. None of that assigns a pCi/L to one foundation. A test does.

What did the IEMA licensed measurements for Lemont show?

In the July 18, 2022 licensed-measurement layer, 543 of 1,354 valid tests with the city name Lemont were at or above 4.0 pCi/L, which is 40.1 percent. A home can appear more than once, and the people who tested chose to test. The IEMA public map uses a different cut, the highest test per address. The file is context. Your test is the decision.

My Lemont home was built after June 1, 2013. Is a passive pipe already there?

The state rule covers new one-family and two-family homes built after that date. The Lemont median year built is 1995, so plenty of homes predate the rule. If you have a pipe and no fan, send a photo. When the builder pipe is usable, Bill adds the fan to it. If it is not usable, he will say so after he looks.

Sources

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