Illinois Private Well Water Risk: Arsenic & Nitrate
These figures are USGS statistical estimates for private (domestic) wells in Illinois. They describe the area's modeled risk — not any single well.
This is a modeled probability for the area, not a measurement of your well. USGS statistical models estimate how many private wells in this area are likely to exceed the federal limit — they cannot tell you what is in your water. Two neighbors can have very different results. The only way to know your well is to test it.
Nitrate
0%
of the private-well population is modeled above the 10 mg/L nitrate limit
~296
people on wells estimated above the limit
~1,120,000
total residents on private wells statewide
Source: USGS machine-learning nitrate model, Ransom et al. (2022), domestic-well depth zone.
Arsenic
Across Illinois, an estimated ~67,710 people rely on private wells with modeled arsenic above the 10 µg/L EPA limit. The highest modeled exposure is in Will County (~8,733 people).
Counties with the highest modeled arsenic exposure
| County | Est. well residents over arsenic limit | 90% range |
|---|---|---|
| Will County | ~8,733 | 7,092–10,811 |
| Kankakee County | ~4,374 | 3,361–5,596 |
| Kendall County | ~3,884 | 3,134–4,816 |
| McHenry County | ~2,904 | 2,420–3,546 |
| Vermilion County | ~2,779 | 2,142–3,548 |
| Sangamon County | ~2,764 | 2,064–3,671 |
| Champaign County | ~2,745 | 2,089–3,531 |
| LaSalle County | ~2,458 | 1,953–3,082 |
| Lake County | ~2,312 | 1,856–2,949 |
| Iroquois County | ~2,138 | 1,680–2,635 |
| Grundy County | ~2,114 | 1,654–2,669 |
| Woodford County | ~1,895 | 1,412–2,484 |
| Livingston County | ~1,819 | 1,411–2,271 |
| Whiteside County | ~1,816 | 1,504–2,248 |
| McLean County | ~1,584 | 1,230–2,020 |
| DeKalb County | ~1,408 | 1,083–1,800 |
| Peoria County | ~1,389 | 1,079–1,782 |
| DuPage County | ~1,104 | 926–1,312 |
| Bureau County | ~1,095 | 831–1,422 |
| Winnebago County | ~1,043 | 888–1,231 |
| Henry County | ~954 | 789–1,156 |
| St. Clair County | ~937 | 738–1,190 |
| Logan County | ~890 | 694–1,132 |
| Ford County | ~742 | 577–924 |
| Edgar County | ~740 | 565–963 |
| Shelby County | ~653 | 503–846 |
| McDonough County | ~628 | 493–795 |
| Douglas County | ~590 | 449–759 |
| Ogle County | ~571 | 478–687 |
| Kane County | ~542 | 436–677 |
| Fulton County | ~541 | 428–685 |
| Boone County | ~524 | 440–623 |
| Piatt County | ~518 | 396–669 |
| Macon County | ~496 | 363–677 |
| De Witt County | ~483 | 371–625 |
| Lee County | ~479 | 388–592 |
| Mercer County | ~461 | 364–582 |
| Tazewell County | ~434 | 344–545 |
| Knox County | ~424 | 348–518 |
| Mason County | ~353 | 267–472 |
| Stark County | ~323 | 253–408 |
| Marshall County | ~319 | 252–402 |
| Moultrie County | ~310 | 237–401 |
| Stephenson County | ~308 | 249–384 |
| Madison County | ~258 | 202–330 |
| Morgan County | ~232 | 184–291 |
| Christian County | ~198 | 127–323 |
| Putnam County | ~191 | 144–250 |
| Warren County | ~190 | 157–232 |
| Carroll County | ~180 | 141–234 |
| Hancock County | ~179 | 139–231 |
| Effingham County | ~146 | 113–189 |
| Cass County | ~142 | 114–178 |
| Cumberland County | ~140 | 111–176 |
| Adams County | ~138 | 95–187 |
| Jo Daviess County | ~137 | 109–176 |
| Fayette County | ~134 | 103–176 |
| Union County | ~123 | 65–209 |
| Monroe County | ~106 | 82–137 |
43 additional Illinois counties have lower modeled arsenic exposure (fewer than 100 estimated well residents over the limit).
Source: USGS domestic-well arsenic model, Lombard et al. (2021); county population product (2017).
Treating arsenic in Illinois
Arsenic is not removed by carbon pitchers or faucet filters. Reverse osmosis is the treatment that brings it below the federal limit at your tap.
We may earn a commission from Amazon at no extra cost to you.