waterbycounty

Illinois Water Quality

Drinking water data for all 102 counties.

Avg Water Score

47.8

State Grade

D

Counties with Data

102

of 102 total

All Illinois Counties

CountyWater Score
Alexander County86.0
Boone County86.0
Brown County86.0
Clay County86.0
Edwards County86.0
Gallatin County86.0
Henderson County86.0
Jasper County86.0
Jefferson County86.0
Jersey County86.0
Marion County86.0
Moultrie County86.0
Washington County86.0
DuPage County71.3
Cook County70.8
Kane County70.1
Kendall County69.3
Coles County68.4
Peoria County68.2
Franklin County67.1
McHenry County67.1
DeKalb County66.0
Stephenson County65.8
Lake County65.3
Will County65.1
Champaign County63.5
Madison County63.4
Crawford County62.8
Tazewell County62.6
St. Clair County61.0
Ogle County60.8
Pike County60.4
White County59.0
Monroe County58.7
Lawrence County58.3
Montgomery County58.3
Winnebago County57.1
De Witt County56.9
Cass County56.8
Wabash County55.4
Mercer County55.3
Vermilion County54.5
Knox County54.4
Rock Island County53.1
Hamilton County52.8
Whiteside County52.3
Warren County50.1
Carroll County48.9
Ford County48.6
Adams County46.6
Sangamon County46.0
Mason County44.4
Jo Daviess County43.2
Macon County42.8
Massac County41.8
Logan County41.6
Grundy County41.2
Pulaski County41.0
Calhoun County40.7
Saline County40.7
Clark County39.8
Kankakee County39.6
McLean County37.2
Shelby County37.1
Cumberland County36.3
Greene County35.3
Livingston County34.4
Hardin County34.2
Piatt County33.4
Edgar County32.0
Williamson County31.6
Stark County31.5
Clinton County31.0
Marshall County30.4
Henry County30.3
Randolph County30.0
Schuyler County30.0
Perry County29.7
Bureau County29.5
Fayette County29.5
Douglas County29.3
Menard County28.3
Jackson County27.5
Iroquois County26.6
Richland County26.4
Morgan County25.0
Hancock County24.7
Putnam County22.6
Woodford County21.0
Lee County20.9
Christian County20.7
McDonough County20.3
Effingham County19.6
Fulton County19.5
Macoupin County16.5
Johnson County15.8
Wayne County15.4
LaSalle County15.3
Pope County12.9
Bond County11.9
Scott County11.9
Union County9.7

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Frequently Asked Questions

Which county in Illinois has the best water quality?
Alexander County has the highest water quality score in Illinois at 86.0/100 (Grade: A), based on EPA SDWIS data.
Which county in Illinois has the most water violations?
Union County has among the lowest water quality scores in Illinois at 9.7/100. See the individual county page for detailed violation history.
Is the tap water safe to drink in Illinois?
Illinois has an average water quality score of 47.8/100 based on EPA Safe Drinking Water Act compliance data. Individual county scores vary — check your specific county's page for detailed information.
What contaminants are found in Illinois water supplies?
Drinking water quality varies by county and water system. The EPA Safe Drinking Water Information System (SDWIS) tracks violations for contaminants like lead, nitrates, bacteria, and disinfection byproducts. See individual county pages for specific contaminant and violation history.

Data Source

Water quality data sourced from the EPA Safe Drinking Water Information System (SDWIS) via the ECHO enforcement database. Scores reflect compliance history and health-based violation counts.

Disclaimer: This data is informational only. It is not health, legal, or professional advice. For concerns about your specific water supply, contact your local water utility.

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