Water quality by county
in Illinois
EPA sampled public water systems across Illinois for PFAS under its UCMR 5 programme. Of the 102 counties, 18 have a reading above a federal limit and 14 have not been sampled at all — which is not a clean result, only an absence of one. Each county below shows what was found, at what concentration, and at which utility.
| county | Population | Worst result | Compound |
|---|---|---|---|
| Madison County | 263,017 | 4.5× | PFOA · 18 ng/L |
| Knox County | 48,716 | 3.5× | PFOA · 14 ng/L |
| Stephenson County | 43,088 | 3.5× | PFOS · 14 ng/L |
| Will County | 708,583 | 3.4× | PFOA · 13.7 ng/L |
| Clinton County | 37,087 | 2.4× | PFOS · 9.4 ng/L |
| McHenry County | 315,959 | 2.1× | PFOA · 8.3 ng/L |
| DuPage County | 937,142 | 1.8× | PFOA · 7.3 ng/L |
| Winnebago County | 283,790 | 1.8× | PFOS · 7.3 ng/L |
| St. Clair County | 251,149 | 1.8× | PFOS · 7 ng/L |
| Peoria County | 179,630 | 1.6× | PFOS · 6.5 ng/L |
| Kane County | 520,997 | 1.4× | PFOA · 5.7 ng/L |
| Logan County | 27,518 | 1.4× | PFOA · 5.7 ng/L |
| Cook County | 5,182,617 | 1.4× | PFOS · 5.5 ng/L |
| Lake County | 718,604 | 1.3× | PFOS · 5 ng/L |
| Wabash County | 10,979 | 1.2× | PFOS · 4.8 ng/L |
| Crawford County | 18,388 | 1.1× | PFOS · 4.6 ng/L |
| Rock Island County | 142,731 | 1.1× | PFOA · 4.6 ng/L |
| Tazewell County | 129,821 | 1.1× | PFOS · 4.4 ng/L |
| Boone County | 53,313 | under the limit | PFHxS · 5.5 ng/L |
| Adams County | 64,109 | under the limit | — |
| Alexander County | 4,594 | not sampled | — |
| Bond County | 16,576 | under the limit | — |
| Brown County | 6,307 | not sampled | — |
| Bureau County | 32,486 | under the limit | — |
| Calhoun County | 4,224 | under the limit | — |
| Carroll County | 15,444 | not sampled | — |
| Cass County | 12,713 | under the limit | — |
| Champaign County | 212,374 | under the limit | — |
| Christian County | 33,247 | under the limit | — |
| Clark County | 15,076 | under the limit | — |
| Clay County | 12,821 | under the limit | — |
| Coles County | 46,423 | under the limit | — |
| Cumberland County | 10,305 | not sampled | — |
| De Witt County | 15,319 | under the limit | — |
| DeKalb County | 101,335 | under the limit | — |
| Douglas County | 19,824 | under the limit | — |
| Edgar County | 16,398 | under the limit | — |
| Edwards County | 5,984 | not sampled | — |
| Effingham County | 34,602 | under the limit | — |
| Fayette County | 21,157 | under the limit | — |
| Ford County | 13,451 | under the limit | — |
| Franklin County | 37,033 | under the limit | — |
| Fulton County | 32,510 | under the limit | — |
| Gallatin County | 4,690 | not sampled | — |
| Greene County | 11,417 | under the limit | — |
| Grundy County | 53,835 | under the limit | — |
| Hamilton County | 7,818 | under the limit | — |
| Hancock County | 17,008 | not sampled | — |
| Hardin County | 3,550 | not sampled | — |
| Henderson County | 6,048 | under the limit | — |
| Henry County | 48,177 | under the limit | — |
| Iroquois County | 26,067 | under the limit | — |
| Jackson County | 53,199 | under the limit | — |
| Jasper County | 9,092 | under the limit | — |
| Jefferson County | 36,107 | under the limit | — |
| Jersey County | 21,150 | under the limit | — |
| Jo Daviess County | 21,528 | under the limit | — |
| Johnson County | 13,320 | not sampled | — |
| Kankakee County | 106,410 | under the limit | — |
| Kendall County | 143,171 | under the limit | — |
| LaSalle County | 108,390 | under the limit | — |
| Lawrence County | 14,801 | under the limit | — |
| Lee County | 33,544 | under the limit | — |
| Livingston County | 35,375 | under the limit | — |
| Macon County | 100,737 | under the limit | — |
| Macoupin County | 43,895 | under the limit | — |
| Marion County | 36,437 | under the limit | — |
| Marshall County | 11,552 | not sampled | — |
| Mason County | 12,543 | under the limit | — |
| Massac County | 13,627 | under the limit | — |
| McDonough County | 26,662 | under the limit | — |
| McLean County | 172,069 | under the limit | — |
| Menard County | 11,963 | under the limit | — |
| Mercer County | 15,292 | under the limit | — |
| Monroe County | 34,969 | under the limit | — |
| Montgomery County | 27,615 | under the limit | — |
| Morgan County | 32,618 | under the limit | — |
| Moultrie County | 14,365 | under the limit | — |
| Ogle County | 51,345 | under the limit | — |
| Perry County | 20,272 | under the limit | — |
| Piatt County | 16,628 | under the limit | — |
| Pike County | 14,258 | under the limit | — |
| Pope County | 3,703 | under the limit | — |
| Pulaski County | 4,879 | not sampled | — |
| Putnam County | 5,633 | not sampled | — |
| Randolph County | 29,903 | under the limit | — |
| Richland County | 15,362 | under the limit | — |
| Saline County | 22,826 | under the limit | — |
| Sangamon County | 194,345 | under the limit | — |
| Schuyler County | 6,750 | not sampled | — |
| Scott County | 4,880 | under the limit | — |
| Shelby County | 20,542 | under the limit | — |
| Stark County | 5,272 | not sampled | — |
| Union County | 16,886 | under the limit | — |
| Vermilion County | 71,106 | under the limit | — |
| Warren County | 16,217 | under the limit | — |
| Washington County | 13,535 | under the limit | — |
| Wayne County | 15,928 | under the limit | — |
| White County | 13,395 | under the limit | — |
| Whiteside County | 54,657 | under the limit | — |
| Williamson County | 67,064 | under the limit | — |
| Woodford County | 38,290 | under the limit | — |