Air Quality Rankings for Illinois 2026

Illinois has 23 cities with EPA air quality data. Macoupin, Illinois has the cleanest air with a 5-year average AQI of 33. Cook, Illinois has the highest AQI at 57.

#	City	5yr Avg AQI	Current AQI	Worst Pollutant	Trend	Grade
1	Macoupin, Illinois	33	37	Ozone	Improving	B
2	Clark, Illinois	34	36	Ozone	Improving	B
3	Jo Daviess, Illinois	34	36	Ozone	Stable	B
4	Effingham, Illinois	39	44	Ozone	Stable	B
5	Adams, Illinois	40	43	Ozone	Worsening	C
6	Lake, Illinois	40	42	Ozone	Worsening	C
7	Kane, Illinois	43	46	Ozone	Worsening	C
8	Randolph, Illinois	45	46	PM2.5	Stable	C
9	Champaign, Illinois	45	48	PM2.5	Worsening	C
10	Jersey, Illinois	46	48	PM2.5	Worsening	C
11	Sangamon, Illinois	46	51	PM2.5	Worsening	D
12	Hamilton, Illinois	46	46	PM2.5	Worsening	C
13	Peoria, Illinois	47	48	PM2.5	Stable	C
14	Rock Island, Illinois	47	51	PM2.5	Worsening	D
15	Winnebago, Illinois	48	52	Ozone	Worsening	D
16	McLean, Illinois	48	50	PM2.5	Worsening	D
17	McHenry, Illinois	49	49	PM2.5	Worsening	C
18	Macon, Illinois	49	51	PM2.5	Worsening	C
19	DuPage, Illinois	49	53	PM2.5	Worsening	D
20	Saint Clair, Illinois	50	54	PM2.5	Worsening	C
21	Will, Illinois	51	53	PM2.5	Stable	C
22	Madison, Illinois	55	55	PM2.5	Worsening	C
23	Cook, Illinois	57	57	PM2.5	Stable	D

Air quality data for Illinois is sourced from the EPA Air Quality System (AQS), which monitors outdoor air quality at thousands of stations nationwide.
— EPA Air Quality System

Frequently Asked Questions

Macoupin, Illinois has the best air quality in Illinois with a 5-year average AQI of 33 and a grade of B.

Illinois has 23 cities with EPA air quality monitoring data in our database, covering multiple years of AQI measurements.

The Air Quality Index (AQI) measures five major pollutants: ground-level ozone, particulate matter (PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide. Lower AQI values indicate cleaner air — 0-50 is "Good," while 150+ is "Unhealthy."

Sources: EPA Air Quality System (AQS)

Cities ranked by 5-year average AQI (lower is better). Grades factor in average AQI, trend direction, unhealthy days, and dominant pollutant.

Cleanest Cities Nationwide →All Air Quality in Illinois →