Well water hardness in Illinois
Across 22 counties of Illinois, the median well sampled by the USGS has 19 gpg of hardness. Counties range from 0.4 gpg (DuPage County) to 27.2 gpg (St. Clair County).
Millions of American households drink water from their own well. No utility tests that water and no water quality report covers it. These pages summarise the hardness the U.S. Geological Survey measured in wells county by county, so you know what to expect before you test your own well.
Counties, hardest first
| gpg | mg/L | wells | ||
|---|---|---|---|---|
| St. Clair County | 27.2 | 465 | 41 | very hard |
| McLean County | 23.3 | 399 | 24 | very hard |
| Madison County | 23.1 | 395 | 47 | very hard |
| McHenry County | 22.7 | 388 | 86 | very hard |
| Fulton County | 22.2 | 380 | 11 | very hard |
| Logan County | 21.7 | 371 | 10 | very hard |
| Ogle County | 21.7 | 371 | 59 | very hard |
| Bureau County | 21.5 | 368 | 82 | very hard |
| Winnebago County | 21.3 | 365 | 20 | very hard |
| Boone County | 20.9 | 358 | 22 | very hard |
| Piatt County | 19.5 | 334 | 15 | very hard |
| DeWitt County | 18.5 | 318 | 24 | very hard |
| Champaign County | 18.5 | 316 | 31 | very hard |
| Peoria County | 18.4 | 314 | 10 | very hard |
| McDonough County | 16 | 275 | 21 | very hard |
| Randolph County | 13.1 | 225 | 21 | very hard |
| Kankakee County | 11.9 | 205 | 10 | very hard |
| Cook County | 0.5 | 8 | 124 | soft |
| Kane County | 0.5 | 8 | 32 | soft |
| Lake County | 0.5 | 8 | 24 | soft |
| Will County | 0.5 | 8 | 26 | soft |
| DuPage County | 0.4 | 8 | 36 | soft |
Counties with fewer than 10 sampled wells, or a median outside 5–500 mg/L, are not shown until the figure is reviewed.
Illinois: tap water hardness by city → · Well water hardness by state and county →