McHenry County, Illinois
AQI 43 · Good43
Median AQI
79
90th Percentile
165
Max AQI
272
Days with Data
Ranked #11 of 23 counties in Illinois (by median AQI, lower is better)
Monthly Median AQI — 2025
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43
Median AQI
79
90th Percentile
165
Max AQI
272
Days with Data
Ranked #11 of 23 counties in Illinois (by median AQI, lower is better)
Click a bar to view that month's details