SmogRank / World / United States / Illinois / September 2025
Most polluted cities in Illinois, United States, September 2025
31 cities in Illinois, United States ranked by their average PM2.5 over the 30 days. Worst: Elmwood Park at 13.6 µg/m³, #365 of 3,052 cities in the world. Cleanest: Winthrop Harbor at 6.5. 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.
- 1Elmwood Parklow-cost sensors 0%
- 2Brookfield 0%
- 3Bridgeview 0%
- 4Wood River 0%
- 5Franklin Park 0%
- 6Granite City 0%
- 7East Saint Louis 0%
- 7Chicago 0%
- 9Lincolnwood 0%
- 10Elgin 0%
- 11Calumet City 0%
- 11Dolton 0%
- 11Peoria 0%
- 14Moline 0%
- 15Des Plaines 0%
- 16Decatur 0%
- 16Upper Alton 0%
- 18Rockford 0%
- 19Springfield 0%
- 19Naperville 0%
- 21Joliet 0%
- 22Warrenville 0%
- 23Oak Lawn 0%
- 24Jerseyville 0%
- 24Bloomington 0%
- 26Savoy 0%
- 27Cary 0%
- 28Champaign 0%
- 29Braidwood 0%
- 29Northbrook 0%
- 31Winthrop 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.
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
All cities in the world, September 2025 · All cities in United States, September 2025 · Illinois now
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SmogRank, most polluted cities in Illinois, United States, PM2.5, September 2025, smogrank.com/us/region/illinois/history/2025-09 (accessed 6 Oct 2026).
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.