Private Well Water Testing in Illinois
County-by-county USGS area-risk estimates for private wells across Illinois — arsenic exceedance probability and private-well population — plus how to test your own well at a Illinois-certified laboratory.
Illinois private-well risk summary
Counties covered
102
Illinois counties with modeled risk data.
People on private wells
area estimate1,120,033
estimated across covered Illinois counties.
Average arsenic risk
area estimate12%
average modeled chance a well exceeds 10 µg/L arsenic across covered counties.
Illinois counties
- Lake County6% arsenic exceedance (area estimate)77,592 people on private wells
- Will County12% arsenic exceedance (area estimate)69,763 people on private wells
- DuPage County5% arsenic exceedance (area estimate)64,010 people on private wells
- Cook County5% arsenic exceedance (area estimate)63,234 people on private wells
- McHenry County10% arsenic exceedance (area estimate)55,636 people on private wells
- Winnebago County6% arsenic exceedance (area estimate)50,808 people on private wells
- Kane County17% arsenic exceedance (area estimate)43,960 people on private wells
- Kankakee County11% arsenic exceedance (area estimate)25,465 people on private wells
- LaSalle County13% arsenic exceedance (area estimate)22,965 people on private wells
- Ogle County6% arsenic exceedance (area estimate)20,627 people on private wells
- Peoria County14% arsenic exceedance (area estimate)19,796 people on private wells
- Whiteside County5% arsenic exceedance (area estimate)19,763 people on private wells
- Tazewell County22% arsenic exceedance (area estimate)18,745 people on private wells
- McLean County35% arsenic exceedance (area estimate)17,215 people on private wells
- DeKalb County11% arsenic exceedance (area estimate)17,175 people on private wells
- Kendall County10% arsenic exceedance (area estimate)17,030 people on private wells
- Rock Island County8% arsenic exceedance (area estimate)16,485 people on private wells
- Macon County53% arsenic exceedance (area estimate)16,392 people on private wells
- Madison County4% arsenic exceedance (area estimate)15,982 people on private wells
- Sangamon County16% arsenic exceedance (area estimate)15,978 people on private wells
- Champaign County25% arsenic exceedance (area estimate)15,717 people on private wells
- St. Clair County10% arsenic exceedance (area estimate)15,098 people on private wells
- Stephenson County3% arsenic exceedance (area estimate)13,275 people on private wells
- Vermilion County15% arsenic exceedance (area estimate)13,059 people on private wells
- Boone County5% arsenic exceedance (area estimate)12,534 people on private wells
- Woodford County37% arsenic exceedance (area estimate)12,248 people on private wells
- Lee County10% arsenic exceedance (area estimate)11,562 people on private wells
- Grundy County9% arsenic exceedance (area estimate)10,801 people on private wells
- Henry County13% arsenic exceedance (area estimate)10,734 people on private wells
- Adams County3% arsenic exceedance (area estimate)10,591 people on private wells
- Iroquois County14% arsenic exceedance (area estimate)9,675 people on private wells
- Fayette County6% arsenic exceedance (area estimate)9,074 people on private wells
- Effingham County3% arsenic exceedance (area estimate)9,015 people on private wells
- Monroe County4% arsenic exceedance (area estimate)9,006 people on private wells
- Livingston County7% arsenic exceedance (area estimate)8,697 people on private wells
- Clinton County6% arsenic exceedance (area estimate)8,594 people on private wells
- Bureau County12% arsenic exceedance (area estimate)8,259 people on private wells
- Fulton County12% arsenic exceedance (area estimate)8,162 people on private wells
- Montgomery County7% arsenic exceedance (area estimate)7,983 people on private wells
- Jo Daviess County13% arsenic exceedance (area estimate)7,967 people on private wells
- Shelby County34% arsenic exceedance (area estimate)7,937 people on private wells
- Knox County10% arsenic exceedance (area estimate)7,571 people on private wells
- Randolph County6% arsenic exceedance (area estimate)7,478 people on private wells
- Macoupin County14% arsenic exceedance (area estimate)7,415 people on private wells
- Logan County46% arsenic exceedance (area estimate)7,330 people on private wells
- Christian County11% arsenic exceedance (area estimate)7,002 people on private wells
- Hancock County4% arsenic exceedance (area estimate)6,961 people on private wells
- Morgan County21% arsenic exceedance (area estimate)6,600 people on private wells
- Mason County15% arsenic exceedance (area estimate)5,999 people on private wells
- Bond County4% arsenic exceedance (area estimate)5,971 people on private wells
- Mercer County10% arsenic exceedance (area estimate)5,856 people on private wells
- McDonough County16% arsenic exceedance (area estimate)5,847 people on private wells
- Carroll County6% arsenic exceedance (area estimate)5,812 people on private wells
- Clark County3% arsenic exceedance (area estimate)5,477 people on private wells
- Wayne County8% arsenic exceedance (area estimate)5,410 people on private wells
- Crawford County3% arsenic exceedance (area estimate)5,395 people on private wells
- Jefferson County7% arsenic exceedance (area estimate)5,316 people on private wells
- Edgar County38% arsenic exceedance (area estimate)5,288 people on private wells
- Warren County9% arsenic exceedance (area estimate)4,943 people on private wells
- Douglas County28% arsenic exceedance (area estimate)4,741 people on private wells
- Jasper County5% arsenic exceedance (area estimate)4,739 people on private wells
- Marion County7% arsenic exceedance (area estimate)4,495 people on private wells
- Richland County5% arsenic exceedance (area estimate)4,442 people on private wells
- Cumberland County6% arsenic exceedance (area estimate)4,440 people on private wells
- Clay County13% arsenic exceedance (area estimate)4,317 people on private wells
- Jackson County7% arsenic exceedance (area estimate)4,238 people on private wells
- Henderson County3% arsenic exceedance (area estimate)4,217 people on private wells
- De Witt County67% arsenic exceedance (area estimate)4,144 people on private wells
- Marshall County25% arsenic exceedance (area estimate)4,034 people on private wells
- Coles County21% arsenic exceedance (area estimate)4,030 people on private wells
- Lawrence County3% arsenic exceedance (area estimate)4,026 people on private wells
- Union County3% arsenic exceedance (area estimate)3,941 people on private wells
- Menard County23% arsenic exceedance (area estimate)3,797 people on private wells
- Greene County12% arsenic exceedance (area estimate)3,766 people on private wells
- Piatt County39% arsenic exceedance (area estimate)3,755 people on private wells
- Moultrie County35% arsenic exceedance (area estimate)3,509 people on private wells
- Massac County8% arsenic exceedance (area estimate)3,217 people on private wells
- Pike County4% arsenic exceedance (area estimate)3,159 people on private wells
- Wabash County3% arsenic exceedance (area estimate)2,839 people on private wells
- Cass County12% arsenic exceedance (area estimate)2,832 people on private wells
- Ford County15% arsenic exceedance (area estimate)2,696 people on private wells
- Washington County9% arsenic exceedance (area estimate)2,692 people on private wells
- White County7% arsenic exceedance (area estimate)2,613 people on private wells
- Hamilton County6% arsenic exceedance (area estimate)2,142 people on private wells
- Pulaski County6% arsenic exceedance (area estimate)2,115 people on private wells
- Stark County36% arsenic exceedance (area estimate)2,075 people on private wells
- Jersey County3% arsenic exceedance (area estimate)2,013 people on private wells
- Alexander County4% arsenic exceedance (area estimate)1,878 people on private wells
- Calhoun County3% arsenic exceedance (area estimate)1,869 people on private wells
- Schuyler County8% arsenic exceedance (area estimate)1,855 people on private wells
- Putnam County14% arsenic exceedance (area estimate)1,785 people on private wells
- Perry County7% arsenic exceedance (area estimate)1,777 people on private wells
- Scott County8% arsenic exceedance (area estimate)1,652 people on private wells
- Johnson County4% arsenic exceedance (area estimate)1,535 people on private wells
- Franklin County4% arsenic exceedance (area estimate)1,282 people on private wells
- Brown County4% arsenic exceedance (area estimate)1,272 people on private wells
- Hardin County4% arsenic exceedance (area estimate)1,223 people on private wells
- Williamson County4% arsenic exceedance (area estimate)981 people on private wells
- Pope County3% arsenic exceedance (area estimate)970 people on private wells
- Saline County7% arsenic exceedance (area estimate)958 people on private wells
- Edwards County12% arsenic exceedance (area estimate)913 people on private wells
- Gallatin County27% arsenic exceedance (area estimate)779 people on private wells
Find a Illinois-certified testing lab
Get your well tested at a Illinois-certified laboratory. We list certification programs by state.
These figures are USGS area estimates: statistical groundwater models describing how likely elevated contaminant levels are across a county. They are not designed to predict the concentration in any single well. Only testing your own well reveals its water quality.
By TapWaterData Editorial
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