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 indexed hardness

285PPM

Very Hard

Indexed range 115–408 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 995 of 1,065 profiles with hardness data. The state median is 285 PPM, but the full indexed range is 115–408 PPM.

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 PPM69

Very hard · 181+ PPM995

Evidence coverage

What the current records support

Hardness estimate: 100%
Lead 90th percentile: 100%
Copper 90th percentile: 23%

340

Low-confidence hardness profiles

336

Nearest site more than 25 miles away

Reported source water

Utility source mix

Groundwater: 691
Surface water: 419
Groundwater influenced by surface water: 7

Highest medians

Hardest indexed cities

1. Hebron408 PPM
2. Richmond405 PPM
3. Harvard401 PPM
4. Roscoe401 PPM
5. Loves Park397 PPM

Lowest medians

Softest indexed cities

1. Cairo115 PPM
2. Brookport135 PPM
3. Mounds145 PPM
4. Vienna155 PPM
5. Goreville155 PPM

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

Search city or county

County

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913 cities found

Page 1 of 39

Abingdon

Knox County · 1 ZIP

282PPM

County	Median	Range	ZIP profiles
Boone County	396 PPM	394–400.5	4
Winnebago County	394 PPM	373.5–400.5	18
Stephenson County	369 PPM	358.5–371.5	6
Ogle County	366 PPM	360–371	10
Mchenry County	360 PPM	360–408	15
Lee County	360 PPM	343–360	11
Peoria County	354 PPM	285–354.5	17
Macon County	354 PPM	307.5–354	13
Dekalb County	351 PPM	323–384.5	12
Pike County	344 PPM	296–365	10
Lawrence County	336 PPM	306–336	3
Jasper County	336 PPM	335–376.5	3

Why local comparisons matter here

Hardness across indexed ZIPs

What the current records support

Utility source mix

Hardest indexed cities

Softest indexed cities

Explore Illinois by city

Abingdon

Addison

Albany

Albion

Aledo

Alexis

Algonquin

Alhambra

Allendale

Allerton

Alma

Alpha

Alsey

Alsip

Altamont

Alton

Altona

Amboy

Anchor

Andalusia

Andover

Anna

Annawan

Antioch

Highest indexed county medians