State distribution
Hardness across indexed ZIPs
Counts describe published ZIP profiles, not a population-weighted statewide sample.
Soft · 0–60 PPM0
Moderately hard · 61–120 PPM1
Hard · 121–180 PPM24
Very hard · 181+ PPM702
State water index
Illinois water hardness
Search 913 indexed communities and 1,065 ZIP profiles, then compare the underlying utility, source, distance, and reporting context.
Median regional evidence
285PPM
Very Hard
Indexed range 71.9–490 PPM
- ZIP profiles
- 1,065
- Cities
- 913
- Matched utilities
- 1,117
- Counties
- 102
Understanding Illinois
Why local comparisons matter here
Illinois includes Lake Michigan supply in the northeast, major river systems, shallow glacial aquifers, and deeper bedrock aquifers across the rest of the state.
In this index, very hard is the largest category, covering 702 of 727 profiles with hardness data. The state median is 285 PPM, but the full indexed range is 71.9–490 PPM.
Evidence coverage
What the current records support
- Hardness estimate
- 68%
- Lead 90th percentile
- 100%
- Copper 90th percentile
- 23%
549
Low-confidence hardness profiles
91
Research-comparison eligible profiles
Reported source water
Utility source mix
- Groundwater
- 691
- Surface water
- 419
- Groundwater influenced by surface water
- 7
Highest medians
Highest eligible city medians
Lowest medians
Lowest eligible city medians
City directory
Explore Illinois by city
Search by city or county, then sort by name, hardness, or ZIP coverage.
913 cities · 1,065 ZIP profiles
913 cities found
Page 1 of 39
Abingdon
Knox County · 1 ZIP
274PPM regional
Single regional valueNo active flag
Addison
Dupage County · 1 ZIP
255PPM regional
Single regional valueNo active flag
Albany
Whiteside County · 1 ZIP
249PPM regional
Single regional value1 active record
Albion
Edwards County · 1 ZIP
—
No regional sampleNo active flag
Aledo
Mercer County · 1 ZIP
274PPM regional
Single regional valueNo active flag
Alexis
Mercer County · 1 ZIP
285PPM regional
Single regional valueNo active flag
Algonquin
Mchenry County · 1 ZIP
401PPM regional
Single regional valueNo active flag
Alhambra
Madison County · 1 ZIP
264PPM regional
Single regional valueNo active flag
Allendale
Wabash County · 1 ZIP
—
No regional sampleNo active flag
Allerton
Vermilion County · 1 ZIP
—
No regional sampleNo active flag
Alma
Marion County · 1 ZIP
—
No regional sampleNo active flag
Alpha
Henry County · 1 ZIP
290PPM regional
Single regional valueNo active flag
Alsey
Scott County · 1 ZIP
—
No regional sampleNo active flag
Alsip
Cook County · 1 ZIP
265PPM regional
Single regional valueNo active flag
Altamont
Effingham County · 1 ZIP
—
No regional sampleNo active flag
Alton
Madison County · 1 ZIP
246PPM regional
Single regional valueNo active flag
Altona
Knox County · 1 ZIP
290PPM regional
Single regional valueNo active flag
Amboy
Lee County · 1 ZIP
—
No regional sampleNo active flag
Anchor
Mclean County · 1 ZIP
287PPM regional
Single regional valueNo active flag
Andalusia
Rock Island County · 1 ZIP
220PPM regional
Single regional valueNo active flag
Andover
Henry County · 1 ZIP
293PPM regional
Single regional valueNo active flag
Anna
Union County · 1 ZIP
145PPM regional
Single regional valueNo active flag
Annawan
Henry County · 2 ZIPs
290PPM regional
Single regional valueNo active flag
Antioch
Lake County · 1 ZIP
408PPM regional
Single regional valueNo active flag
County comparison
Highest regional-evidence county medians
| County | Median | Range | ZIP profiles |
|---|---|---|---|
| Madison County | 490 PPM | 245.5–490 | 19 |
| Mcdonough County | 433 PPM | 353.5–433 | 8 |
| Mchenry County | 401 PPM | 394–408 | 15 |
| Boone County | 394 PPM | 394–394 | 4 |
| Adams County | 360 PPM | 206–360 | 10 |
| Pike County | 360 PPM | 360–360 | 10 |
| Kane County | 351 PPM | 255–417 | 16 |
| Hamilton County | 349 PPM | 349–349 | 3 |
| White County | 349 PPM | 177–418 | 7 |
| Gallatin County | 347 PPM | 345–347 | 5 |
| Saline County | 347 PPM | 334.5–347 | 6 |
| Moultrie County | 344 PPM | 335–352 | 4 |