Your county health department
Illinois doesn't run a statewide free testing program that we know of. Some county health departments test wells or sell kits, so call yours first.
Illinois's private well pageNitrate in Illinois well water, by county
Nitrate is widespread, over the limit in 15% or more of tested wells, in 6 of the 10 Illinois counties with 10 or more tested wells. A county's share tells you how likely a problem is nearby. Only a test of your own well tells you what's in it.
How Illinois compares with the rest of the country
Across Illinois, about 2 in 10 tested wells had nitrate over the EPA limit of 10 mg/L (79 of 423). Across all tested wells in the US it's about 1 in 12. So nitrate turns up in Illinois wells about twice as often as in the country as a whole, and a test is worth adding even if your county isn't on the list below.
Why it matters: It's dangerous for babies under 6 months, because it keeps their blood from carrying enough oxygen.
Nitrate soaks down into groundwater from fertilizer, manure and septic systems.
Nitrate in tested wells, county by county
Share of each county's tested wells with at least one result over the EPA limit of 10 mg/L. Counties need 10 or more tested wells to be listed. Widespread means 15% or more, worth checking 5 to 15%, rare under 5%.
| County | Wells tested | Wells over the limit | Level |
|---|---|---|---|
| Tazewell County | 12 | Widespread | |
| Mason County | 27 | Widespread | |
| Ogle County | 10 | Widespread | |
| Kankakee County | 14 | Widespread | |
| St. Clair County | 17 | Widespread | |
| Madison County | 12 | Widespread | |
| McLean County | 15 | Worth checking | |
| McHenry County | 74 | Worth checking | |
| De Witt County | 13 | Rare | |
| Champaign County | 10 | Rare |
70 more Illinois counties have 1 to 9 tested wells for nitrate, too few to rate.
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Where to get your well tested for nitrate in Illinois
A lab Illinois certifies
Ask for nitrate by name. Results from a certified lab count for a home sale or a loan.
Labs certified by IllinoisA mail-in kit
Fill the bottles at your kitchen tap and mail them back. We mark the kits that include nitrate.
Compare kitsKeep reading about wells in Illinois
- Well water testing in Illinois: how to get tested and what turns up statewide
- Nitrate in well water: where it comes from, what it does and how to remove it
- Manganese in Illinois wells, by county
Questions people ask about nitrate in Illinois
Is there nitrate in Illinois well water?
Nitrate is widespread, over the limit in 15% or more of tested wells, in 6 of the 10 Illinois counties with 10 or more tested wells. Across Illinois, about 2 in 10 tested wells had nitrate over the EPA limit of 10 mg/L (79 of 423). Across all tested wells in the US it's about 1 in 12. So nitrate turns up in Illinois wells about twice as often as in the country as a whole, and a test is worth adding even if your county isn't on the list below.
Where can I get my well tested for nitrate in Illinois?
Use a lab certified by Illinois for drinking water, or a mail-in kit that includes nitrate from a certified lab. Some county health departments test wells too, so call yours first.
See Illinois's list of certified labs, or compare mail-in kits.
Where these numbers come from
- Lab tests: Water Quality Portal (USGS and EPA), well samples since 2000. A well counts as over if any of its tests was over the EPA limit of 10 mg/L. Wells tested for studies and monitoring, not a random sample of homes.
- Likely overstated: our own check of who tested the wells, when and where. How we check.
- State programs and links: Illinois Department of Public Health.