Well water in Iroquois County, Illinois

Name: Private well water quality in Iroquois County, Illinois
Creator: Well Water Nerd
License: Public domain (US federal government data)

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Testing strongly recommended

tested well samples in Iroquois County exceeded the EPA limit for arsenic (10 ug/L), based on public data from USGS Water Quality Portal.

544 test results across 14 contaminants from at least 41 wells, 1984 to 2021; nitrate has the most at 64. Data refreshed September 15, 2026.

Compiled by Nick at Well Water Nerd from public records. How these pages are built

An estimated 8,825 people in Iroquois County get their drinking water from a private well, per USGS 2015 county water use. That is about 31% of residents.

Separately, the USGS national arsenic model estimates that 24% of the 8,825 people on private wells in Iroquois County draw water above 10 ug/L (the model's range is 19% to 30%), from geology and well depth rather than local tests.

What individual samples found

Each row summarizes every public sample for that contaminant inside Iroquois County. Above limit means above the EPA maximum contaminant level; where EPA has no enforceable limit, the row shows a health guideline or nuisance level instead.

Contaminant	Above limit	Samples	Detected	Median	Highest	Limit
Arsenic 1984 to 2021	22%	59	49%	0	52	10 ug/L EPA limit
Nitrate 1984 to 2021	0%	64	19%	0	0.49	10 mg/L EPA limit
Copper 1984 to 2021	0%	59	12%	0	0.07	1.3 mg/L EPA limit
Lead 1984 to 2021	0%	58	9%	0	0.089	15 ug/L EPA limit
Fluoride 1984 to 2021	0%	58	98%	0.3	3.5	4 mg/L EPA limit
Manganese 1984 to 2021	no limit	60	98%	30	320	300 ug/L health guideline
Sodium 1984 to 2021	no limit	59	100%	56	120	20 mg/L health guideline
Iron 1984 to 2021	no limit	59	97%	1,420	3,570	300 ug/L nuisance level
Chloride 1984 to 2021	no limit	58	93%	9.25	80	250 mg/L nuisance level

Sampled fewer than 10 times, too few to summarize: Uranium (5), PFOS (1), Radium (226 + 228) (1), PFOA (1), Radon (2).

Closer than the county

See the sampled wells near your address

The same records, drawn around one point: which wells within a few miles were sampled and what they found, how deep the wells next to you were drilled, and any leaking tank or cleanup site within a mile.

Check my address

What this means

The contaminants most often above their limit here are arsenic (22% of 59 samples). A well next door can differ sharply from yours because bedrock fractures, well depth and plumbing all matter, so these rates describe the area, not your tap.

Manganese, Iron, and Chloride are widespread in local groundwater. They are mainly a staining and taste problem, but high manganese also carries a health advisory for infants.

What to test for in Iroquois County

1
Arsenic
22% of 59 local samples were above the limit.
2
Coliform bacteria
Recommended for every private well, every year.
3
Radon
Median local reading is 230 pCi/L.
4
Nitrate
Recommended for every private well, especially near farms or septic systems.
5
Manganese
Detected in 98% of local samples.
6
Fluoride
Detected in 98% of local samples.
7
Iron
Detected in 97% of local samples.

Test your Iroquois County well for arsenic, coliform bacteria and radon

Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.

Order the Tap Score well water test kit, from $209 Already tested? Upload the report

Just want bacteria checked first? Tap Score coliform and E. coli test, $99. Coliform and E. coli are the tests every well needs every year.

Want a quick look before paying for a lab? Home well water test strips on Amazon check hardness, iron, pH and nitrate in minutes. They are a screen, not a result: arsenic, bacteria, uranium and PFAS need a certified lab.

Affiliate links: the merchant pays us a commission and the price is the same for you. It does not change what the data above says. As an Amazon Associate we earn from qualifying purchases.

Where to get a well tested in Illinois: certified labs, state programs and prices.

Already have results back? Get your lab report read against the Iroquois County numbers, $29. Every line explained, ranked by what matters, with the fix for each.

The rock under Iroquois County

Silurian-Devonian aquifers

Carbonate-rock. Limestone and dolomite move water through cracks and solution channels, sometimes very fast. Bacteria and nitrate can travel from the surface to a well in days, so annual bacteria testing matters more here than most places; hardness is a given.

Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the county centroid. A single well can sit in a different unit, especially near a boundary.

Official help in Illinois

Two places to start that are not selling anything: the state program that answers private well questions, and its list of labs certified to run drinking water tests. A certified lab is the difference between a result you can act on and a number.

Private Water & Closed Loop Wells, IDPH
Accredited Labs, Illinois EPA

Treatment that fits the local profile

Arsenic

Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange

Manganese

Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis

Iron

Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration

Systems we would look at first

Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.

For arsenic

Under-sink reverse osmosis system

under-sink or countertop, about $300

Look for NSF/ANSI 58 certification listing the contaminant you need removed.

For arsenic

Whole-house arsenic and uranium filter

whole-house, at the point of entry, about $2,500

Adsorptive iron-based media; sized to your well yield.

For arsenic

Aquasana SmartFlow reverse osmosis

under-sink or countertop, about $225

Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.

For manganese

Iron and manganese oxidizing filter

whole-house, at the point of entry, about $1,800

Air-injection or greensand media; fixes staining at the source.

Free, no obligation

Get on the list for a free in-home water test in Iroquois County

No water treatment company serves Iroquois County through Well Water Nerd yet. We are signing licensed companies on county by county: they test at your tap for free, walk you through the numbers, and quote treatment only if something needs fixing. Leave your details and you are first in line. Nothing is shared until a company joins for Iroquois County, and you get an email naming it first.

Common questions

Is there arsenic in well water in Iroquois County?

Arsenic was detected in 49% of 59 public well samples in Iroquois County, and 22% were above the EPA limit of 10 ug/L. Arsenic has no taste or smell; a lab test is the only way to know your level.

How often should I test a private well in Iroquois County?

Test for bacteria and nitrate every year. Test once for arsenic, uranium, radon, fluoride, manganese and PFAS, then again every three to five years or after any change in taste, color, or plumbing.

Counties near Iroquois County

Closest first. Groundwater does not stop at a line on a map, so the next county over is a fair second opinion.

Want the numbers themselves? Download the Illinois dataset as CSV, every county and town, with the sources named.

Sources

USGS Water Quality Portal: 544 samples in Iroquois County. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
USGS national arsenic model (Ayotte 2017): estimated share of 8,825 people on private wells in Iroquois County above 10 ug/L of arsenic, from geology, well depth and land use. County estimates of domestic well users with arsenic above 10 ug/L from the USGS national logistic regression model (Ayotte, Medalie and Qi, 2017), with private well population from the USGS 2015 county water-use compilation (Dieter and others, 2018). Retrieved September 15, 2026.

Non-detects count as samples and are treated as zero when computing medians. Exactly at the limit counts as not above it. A sample belongs to the town containing the well's reported coordinates.