Air Quality in Illinois

Illinois has 23 counties with EPA air quality monitoring. Air quality is generally worsening across the state, with an average of 246 "Good" days per county per year. The best air quality is in Macoupin (median AQI 35) and the most polluted is Cook (median AQI 54).

County	Median AQI	Max AQI	Good Days	Unhealthy Days	Trend	Top Pollutant
Adams	42	97	210	0	→ stable	Ozone
Champaign	44	100	250	0	→ stable	Ozone
Clark	36	90	332	0	→ stable	Ozone
Cook	54	166	131	11	→ stable	PM2.5
DuPage	45	97	230	0	→ stable	PM2.5
Effingham	41	101	217	1	→ stable	Ozone
Hamilton	44	112	236	1	→ stable	PM2.5
Jersey	42	112	248	1	→ stable	Ozone
Jo Daviess	36	101	327	1	→ stable	Ozone
Kane	42	105	237	1	↑ worsening	Ozone
Lake	40	140	201	5	↑ worsening	Ozone
Macon	43	101	238	1	→ stable	PM2.5
Macoupin	35	105	342	1	↓ improving	Ozone
Madison	49	165	193	6	→ stable	PM2.5
McHenry	43	108	245	1	→ stable	PM2.5
McLean	44	112	254	1	→ stable	PM2.5
Peoria	44	100	236	0	→ stable	PM2.5
Randolph	40	100	289	0	→ stable	PM2.5
Rock Island	44	84	277	0	↑ worsening	PM2.5
Saint Clair	46	112	218	3	→ stable	PM2.5
Sangamon	41	105	263	1	→ stable	PM2.5
Will	44	84	245	0	→ stable	PM2.5
Winnebago	43	119	249	3	↑ worsening	PM2.5