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Not health advice. Contact your local water utility for concerns.
Data from EPA Water Quality Reports. For official information, contact your water utility or health department.
Compare water quality across 20 counties in Illinois
20 counties ranked by average water quality score
| Rank | County | Avg Score | Grade | Cities | Population | Score Range |
|---|---|---|---|---|---|---|
| 1 | Peoria County | 96 | A+ | 1 | 113,150 | 96 - 96 |
| 2 | Adams County | 90 | A | 1 | 39,463 | 90 - 90 |
| 3 | Knox County | 87 | A- | 1 | 29,141 | 87 - 87 |
| 4 | Will County | 86 | A- | 4 | 310,308 | 67 - 98 |
| 5 | Madison County | 86 | A- | 1 | 27,549 | 86 - 86 |
| 6 | Champaign County | 85 | A- | 2 | 130,516 | 80 - 89 |
| 7 | DuPage County | 82 | B+ | 7 | 420,618 | 70 - 97 |
| 8 | Macon County | 82 | B+ | 1 | 70,522 | 82 - 82 |
| 9 | Winnebago County | 82 | B+ | 1 | 148,655 | 82 - 82 |
| 10 | Sangamon County | 82 | B+ | 1 | 114,394 | 82 - 82 |
| 11 | Lake County | 81 | B+ | 4 | 192,064 | 74 - 85 |
| 12 | McHenry County | 81 | B+ | 2 | 70,794 | 68 - 94 |
| 13 | Kane County | 79 | B | 4 | 364,428 | 55 - 92 |
| 14 | Rock Island County | 79 | B | 2 | 79,668 | 69 - 89 |
| 15 | Cook County | 78 | B | 22 | 3,926,957 | 47 - 94 |
| 16 | Vermilion County | 76 | B | 1 | 30,479 | 76 - 76 |
| 17 | McLean County | 70 | B- | 2 | 132,944 | 69 - 70 |
| 18 | DeKalb County | 67 | C+ | 1 | 43,849 | 67 - 67 |
| 19 | St. Clair County | 53 | D | 1 | 41,097 | 53 - 53 |
| 20 | Kendall County | 51 | D | 1 | 34,485 | 51 - 51 |
1 cities • 113,150 residents
1 cities • 39,463 residents
1 cities • 29,141 residents
4 cities • 310,308 residents
1 cities • 27,549 residents
2 cities • 130,516 residents
7 cities • 420,618 residents
1 cities • 70,522 residents
1 cities • 148,655 residents
1 cities • 114,394 residents
4 cities • 192,064 residents
2 cities • 70,794 residents
See all 20 counties in the ranking table above
Our county-level water quality analysis aggregates data from municipal water systems across Illinois. Each county's score represents the average water quality across all analyzed cities within that county, weighted by population served.
With 20 counties and 60 cities analyzed, this data helps residents understand regional water quality patterns in Illinois. County scores range from 47/100 to 98/100, reflecting the diversity of water sources and treatment infrastructure across the state.
Currently, 3 counties in Illinois have average scores below 70, indicating potential water quality concerns. Residents in these areas should review their city's specific report and consider water filtration options.