Quick answer
About 1,121,000 people in Illinois (8.7% of residents) got their water from private wells in 2010, according to USGS estimates. Illinois Department of Public Health runs the state’s private well guidance. We didn’t find a free statewide well testing program in Illinois. Certified labs charge for each test, and some county health departments offer lower-cost bacteria and nitrate tests.
- People on private wells
- 1,120,648
- Share of residents
- 8.7%
- Rank among states
- 13th
- Well users modeled above 10 µg/L arsenic
- 11.7%
Where to get your well tested in Illinois
- Illinois Department of Public Health: Private Water & Closed Loop Wells, the state’s guidance for private well owners.
- Well water testing in Illinois: what to test for and how to collect a sample.
- Certified laboratories in Illinois. Use a lab certified for drinking water, so results are reliable.
Free or low-cost testing
We didn’t find a free statewide program in Illinois. Certified labs charge per test; county health departments sometimes offer lower-cost bacteria and nitrate tests.
Mail-in lab kits are another option when no local lab is convenient. See well water test kits for what home kits can and can’t tell you.
What to test for
- Every year: total coliform bacteria and nitrate.
- Before buying equipment: pH, hardness, iron, manganese and, if there’s a smell, hydrogen sulfide.
- Based on location: arsenic, uranium and radon, PFAS, and lead in older plumbing.
USGS modeling estimates that about 11.7% of Illinois’s private well users have water above the 10 µg/L arsenic limit. Arsenic has no taste or smell, so include it in your first test.
Private wells by county
Estimated people relying on private wells in each Illinois county in 2010, the share of residents that represents, and the modeled share of well users with arsenic above 10 µg/L. These are USGS model estimates (2010 population), not measurements of any well. Arsenic is hidden for counties with fewer than 500 well users.
| County | People on wells | Share | Arsenic >10 µg/L |
|---|---|---|---|
| Lake County | 77,769 | 11.1% | 6.0% |
| Will County | 69,696 | 10.3% | 12.5% |
| DuPage County | 63,780 | 7.0% | 5.1% |
| Cook County | 63,411 | 1.2% | 3.8% |
| McHenry County | 55,909 | 18.1% | 10.2% |
| Winnebago County | 50,794 | 17.2% | 5.1% |
| Kane County | 43,980 | 8.5% | 14.8% |
| Kankakee County | 25,545 | 22.5% | 10.9% |
| LaSalle County | 22,926 | 20.1% | 11.7% |
| Ogle County | 20,593 | 38.5% | 5.9% |
| Peoria County | 19,757 | 10.6% | 14.8% |
| Whiteside County | 19,752 | 33.8% | 4.5% |
Show all 102 counties
| Tazewell County | 18,788 | 13.9% | 21.1% |
| McLean County | 17,237 | 10.2% | 42.4% |
| DeKalb County | 17,209 | 16.4% | 11.6% |
| Kendall County | 16,947 | 14.8% | 9.1% |
| Rock Island County | 16,596 | 11.2% | 7.6% |
| Macon County | 16,430 | 14.8% | 56.9% |
| Sangamon County | 15,985 | 8.1% | 15.4% |
| Madison County | 15,906 | 5.9% | 3.6% |
| Champaign County | 15,737 | 7.8% | 28.3% |
| St. Clair County | 15,206 | 5.6% | 9.6% |
| Stephenson County | 13,303 | 27.9% | 3.0% |
| Vermilion County | 13,020 | 16.0% | 17.1% |
| Boone County | 12,585 | 23.2% | 5.4% |
| Woodford County | 12,250 | 31.7% | 35.3% |
| Lee County | 11,549 | 32.1% | 9.2% |
| Henry County | 10,791 | 21.4% | 13.3% |
| Grundy County | 10,746 | 21.5% | 8.8% |
| Adams County | 10,598 | 15.8% | 2.9% |
| Iroquois County | 9,582 | 32.2% | 13.2% |
| Fayette County | 9,090 | 41.1% | 6.3% |
| Effingham County | 8,999 | 26.3% | 3.0% |
| Monroe County | 8,957 | 27.2% | 3.4% |
| Livingston County | 8,717 | 22.4% | 6.9% |
| Clinton County | 8,610 | 22.8% | 6.2% |
| Bureau County | 8,269 | 23.6% | 12.3% |
| Fulton County | 8,170 | 22.0% | 12.3% |
| Jo Daviess County | 8,021 | 35.4% | 11.6% |
| Montgomery County | 8,008 | 26.6% | 7.2% |
| Shelby County | 7,979 | 35.7% | 32.8% |
| Knox County | 7,590 | 14.3% | 9.5% |
| Randolph County | 7,468 | 22.3% | 5.0% |
| Macoupin County | 7,390 | 15.5% | 14.1% |
| Logan County | 7,346 | 24.2% | 46.6% |
| Hancock County | 7,101 | 37.2% | 4.4% |
| Christian County | 6,982 | 20.1% | 12.1% |
| Morgan County | 6,602 | 18.6% | 21.1% |
| Bond County | 5,958 | 33.5% | 3.7% |
| Mason County | 5,932 | 40.4% | 14.0% |
| Mercer County | 5,864 | 35.7% | 10.7% |
| McDonough County | 5,844 | 17.9% | 16.6% |
| Carroll County | 5,807 | 37.7% | 5.8% |
| Clark County | 5,486 | 33.6% | 3.0% |
| Crawford County | 5,415 | 27.3% | 3.4% |
| Wayne County | 5,413 | 32.3% | 8.3% |
| Jefferson County | 5,366 | 13.8% | 6.7% |
| Edgar County | 5,293 | 28.5% | 38.8% |
| Warren County | 4,915 | 27.8% | 9.2% |
| Jasper County | 4,751 | 49.0% | 4.5% |
| Douglas County | 4,718 | 23.6% | 31.0% |
| Marion County | 4,504 | 11.4% | 7.5% |
| Richland County | 4,446 | 27.4% | 5.4% |
| Cumberland County | 4,416 | 40.0% | 6.0% |
| Clay County | 4,322 | 31.3% | 12.2% |
| Jackson County | 4,237 | 7.0% | 6.5% |
| De Witt County | 4,144 | 25.0% | 67.9% |
| Henderson County | 4,113 | 56.1% | 2.3% |
| Coles County | 4,071 | 7.6% | 20.5% |
| Marshall County | 4,059 | 32.1% | 24.7% |
| Lawrence County | 4,001 | 23.8% | 2.9% |
| Union County | 3,946 | 22.2% | 3.3% |
| Menard County | 3,827 | 30.1% | 22.4% |
| Greene County | 3,775 | 27.2% | 11.9% |
| Piatt County | 3,743 | 22.4% | 39.2% |
| Moultrie County | 3,598 | 24.2% | 34.6% |
| Massac County | 3,192 | 20.7% | 7.7% |
| Pike County | 3,186 | 19.4% | 4.2% |
| Wabash County | 2,841 | 23.8% | 3.0% |
| Cass County | 2,832 | 20.8% | 11.4% |
| Washington County | 2,707 | 18.4% | 8.9% |
| Ford County | 2,684 | 19.1% | 14.6% |
| White County | 2,629 | 17.9% | 7.5% |
| Hamilton County | 2,141 | 25.3% | 6.3% |
| Pulaski County | 2,110 | 34.3% | 6.0% |
| Stark County | 2,057 | 34.3% | 36.1% |
| Jersey County | 2,023 | 8.8% | 3.4% |
| Schuyler County | 1,868 | 24.8% | 7.8% |
| Alexander County | 1,857 | 22.5% | 3.2% |
| Calhoun County | 1,828 | 35.9% | 3.0% |
| Perry County | 1,783 | 8.0% | 6.9% |
| Putnam County | 1,769 | 29.5% | 14.0% |
| Scott County | 1,636 | 30.5% | 8.0% |
| Johnson County | 1,540 | 12.2% | 4.2% |
| Brown County | 1,272 | 18.3% | 3.9% |
| Franklin County | 1,225 | 3.1% | 3.5% |
| Hardin County | 1,215 | 28.1% | 3.4% |
| Williamson County | 987 | 1.5% | 4.0% |
| Pope County | 979 | 21.9% | 2.7% |
| Saline County | 953 | 3.8% | 7.6% |
| Edwards County | 917 | 13.6% | 11.6% |
| Gallatin County | 777 | 13.9% | 27.0% |
Counties with the highest modeled arsenic share: De Witt County (67.9%), Macon County (56.9%), Logan County (46.6%), McLean County (42.4%), Piatt County (39.2%).
After you get results
Enter your numbers in the test results tool to see what needs treating and in what order. The guide to reading a well water test explains units and limits.
Common questions
Does Illinois offer free well water testing?
We didn’t find a free statewide well testing program in Illinois. Certified labs charge for each test, and some county health departments offer lower-cost bacteria and nitrate tests.
Who oversees private wells in Illinois?
Illinois Department of Public Health (Private Water & Closed Loop Wells) publishes guidance for private well owners. Private wells aren’t covered by the federal Safe Drinking Water Act, so testing and treatment are up to the owner.
How many people use private wells in Illinois?
USGS estimates about 1,121,000 people, or 8.7% of the population in 2010. That ranks 13th of the states covered by the estimate.
What should I test my well for in Illinois?
Test every year for total coliform bacteria and nitrate, plus pH, hardness, iron and manganese before buying equipment. Arsenic is a known concern in parts of Illinois, so add it to the first test.
Sources
- Illinois Department of Public Health: Private Water & Closed Loop Wells
- Illinois Department of Public Health: well water testing
- Illinois certified laboratories
- USGS data release: domestic well locations and populations served, 2000 and 2010 (Johnson, Belitz and Lombard, 2019)
- CDC Environmental Public Health Tracking: private well water data (from USGS)