Air quality · Illinois
Air quality in Illinois
Across the 8 Illinois ZIPs with EPA county air-quality data, the median day ranges from Good to Moderate (median AQI 42–53). 28 days across those counties reached Unhealthy or worse in 2025. This is a 2025 county annual summary, not a live reading.
Last verified 2026-09-24 · methodology
Air quality by ZIP code in Illinois
EPA's 2025 annual summary for each ZIP's county. Median AQI is the typical day; lower is cleaner.
| ZIP | Median AQI | Good days | Unhealthy or worse |
|---|---|---|---|
| 60601ChicagoCook County | 53 Moderate | 149 of 365 | 5 |
| 60614Chicago (Lincoln Park)Cook County | 53 Moderate | 149 of 365 | 5 |
| 61602PeoriaPeoria County | 45 Good | 214 of 357 | 2 |
| 60302Oak ParkCook County | 53 Moderate | 149 of 365 | 5 |
| 60611Chicago (Streeterville)Cook County | 53 Moderate | 149 of 365 | 5 |
| 61820ChampaignChampaign County | 43 Good | 240 of 365 | 0 |
| 60201Evanston (IL)Cook County | 53 Moderate | 149 of 365 | 5 |
| 60515Downers GroveDuPage County | 42 Good | 233 of 365 | 1 |
County-level figures from EPA Air Quality System (AQS), annual county summary, joined to each ZIP by county. None of them is a measurement at a specific address.
What lands here
Pages show the 2025 median AQI category (Good, Moderate, Unhealthy for Sensitive Groups, Unhealthy, Very Unhealthy, Hazardous) for the ZIP's county, plus the year's max/90th-percentile AQI and day-count breakdown by category.
Source & refresh
EPA Air Quality System (AQS), annual county summary. Refreshed annual (epa aqs publication). Primary source →
Illinois top concern
Lead service lines, flooding (Mississippi/Illinois)
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See Illinois state page for the full state-level rollup across all 12 dimensions.
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