SmogRank / World / United States / Illinois / September 2026

Most polluted cities in Illinois, United States, September 2026

37 cities in Illinois, United States ranked by their average PM2.5 over the 30 days. Worst: Granite City at 9.8 µg/m³, #673 of 2,949 cities in the world. Cleanest: Winthrop Harbor at 4.9. A city needs measurements on 70% of the days to be ranked.

Ranked by unhealthy days: the share of each city's measured days with a daily mean over 35.4 µg/m³ (US AQI 101+), Unhealthy for Sensitive Groups or worse on the US EPA's scale. Ties go to the higher average.

← Granite City 0% 0.75%0
Every city in Illinois, United States ranked for September 2026, one column each, ranked by unhealthy days: height is the share of its measured days that were unhealthy, colour its average. Point at it to read a city; tap to open it.
  1. 1Granite City
    0%
  2. 2Wood River
    0%
  3. 3Upper Alton
    0%
  4. 3Bridgeview
    0%
  5. 5East Saint Louis
    0%
  6. 6Blue Islandlow-cost sensors
    0%
  7. 6Elmwood Parklow-cost sensors
    0%
  8. 8Calumet City
    0%
  9. 8Franklin Park
    0%
  10. 8Oak Lawn
    0%
  11. 11Evergreen Parklow-cost sensors
    0%
  12. 12Skokielow-cost sensors
    0%
  13. 13Nileslow-cost sensors
    0%
  14. 14Evanstonlow-cost sensors
    0%
  15. 14Naperville
    0%
  16. 14Park Ridgelow-cost sensors
    0%
  17. 17Brookfield
    0%
  18. 17Peoria
    0%
  19. 19Decatur
    0%
  20. 20Dolton
    0%
  21. 21Chicago
    0%
  22. 22Jerseyville
    0%
  23. 22Champaign
    0%
  24. 22Elgin
    0%
  25. 25Springfield
    0%
  26. 26Bloomington
    0%
  27. 26Northbrook
    0%
  28. 28Lincolnwood
    0%
  29. 29Rockford
    0%
  30. 29Warrenville
    0%
  31. 31Joliet
    0%
  32. 32Savoy
    0%
  33. 33Braidwood
    0%
  34. 34Moline
    0%
  35. 35Cary
    0%
  36. 35Des Plaines
    0%
  37. 37Winthrop Harbor
    0%

Low-cost sensors: consumer units, counted only in cities with no government-grade monitor; they read close to reference monitors on the whole, but 15 to 25% high in humid air. How we use them.

Good0–50
Moderate51–100
Sensitive groups101–150
Unhealthy151–200
Very unhealthy201–300
Hazardous301+

The US EPA's Air Quality Index for PM2.5 (2024 breakpoints). Show values as: µg/m³ · US AQI · India AQI · China AQI · European AQI · UK DAQI · Canada AQHI+. About the scales

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SmogRank, most polluted cities in Illinois, United States, PM2.5, September 2026, smogrank.com/us/region/illinois/history/2026-09 (accessed 6 Oct 2026).

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You're welcome to reuse a single chart, image or figure with this citation and a link. Terms. Raw monitor readings in bulk are published by OpenAQ, under each provider's licence.