Mchenry County, Illinois: drinking water report. McHenry County in northeastern Illinois has a population of about 310,000 and sits in the outer ring of
McHenry County in northeastern Illinois has a population of about 310,000 and sits in the outer ring of the Chicago metro area. Unlike Cook and DuPage Counties, which rely on Lake Michigan water, McHenry County draws entirely from groundwater – primarily from deep sandstone aquifers and shallower sand-and-gravel deposits. The county's rapid suburbanization over the past three decades has increased water demand and introduced new contamination sources over formerly agricultural land.
The combination of increasing pumping and finite aquifer capacity has lowered water levels in the deep sandstone aquifer beneath McHenry County by over 100 feet since the 1950s. According to the Illinois State Water Survey's 2024 assessment, some communities in the county are approaching the practical limits of their current wells and may need to develop new sources or join the Lake Michigan supply system.
Radium – a naturally occurring radioactive element that concentrates in sandstone aquifer water as levels drop – is a compliance challenge. The Illinois EPA's 2024 monitoring data shows that three public water systems in McHenry County have exceeded the EPA's MCL of 5 pCi/L for combined radium. The EPA's UCMR5 data also shows PFAS detections at low levels across several county systems.
Radium in McHenry County's water is colorless, odorless, and tasteless – you cannot detect it without testing. If your system has reported radium above the MCL, point-of-use treatment is available while the system works toward compliance.
Check your water for current data on your system. For radium, ion exchange softeners or reverse osmosis are effective. For PFAS, RO handles both. Our water filter guide covers well-water-specific options. Pull your detailed report for historical trends, and visit our Illinois page for statewide context.
Drinking water is one exposure route. These federal datasets also cover Mchenry County, IL.
The EPA places Mchenry County, IL in Zone 2 - a moderate-risk category, with a predicted average indoor radon level between 2 and 4 pCi/L. Zone maps predict an area's radon potential from geology and existing indoor readings; they say nothing about a specific house. Testing is the only way to know your own level.
39% of homes in Mchenry County, IL were built before 1980, and 11% before 1950. Residential lead paint was banned in 1978, so housing age is the strongest available proxy for lead-paint exposure. This describes the county's housing stock, not any one home.
Modelled annual fine-particle pollution (PM2.5) in Mchenry County, IL averages 8.6 µg/m³, within the EPA's annual standard of 9 µg/m³. These are CDC modelled county estimates rather than readings from a specific monitor.
How radon zones work · Air quality by county · Lead exposure guide
18 public water systems serving McHenry County, IL have EPA lead testing on record. The reported lead sample skews toward systems that already flagged a problem, so its exceedance rate is not directly comparable with other areas. 13 water systems serving McHenry County, IL carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Lead and Copper Rule | 9 |
| Barium | 1 |
| Revised Total Coliform Rule | 1 |
| Manganese | 1 |
| Lead and Copper Rule Revisions | 1 |
Source: EPA Lead and Copper Rule 90th-percentile tap sampling and EPA SDWIS Safe Drinking Water Act enforcement records, aggregated from the public water systems serving this county. Figures are counts of water systems, not a test of any individual home or tap.