Data / Median Air Quality Index (US EPA) / Cook County

Median Air Quality Index (US EPA) in Cook County

Median Air Quality Index (US EPA) in Cook County was 53 in 2025, according to the U.S. Environmental Protection Agency. That is down 1 from 2024. That is the 1st highest of 23 counties in 2025.

2025, index53
Change on 2024-1
Rank1st of 23Counties in Illinois ranked
Series high771980
Series low501991

Next release: Tuesday, 13 July 2027, estimated by Invokely from past publication dates (low confidence), not announced by the publisher. Release calendar

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Median Air Quality Index (US EPA) in Cook County, 1980 to 2025

5060708019801987199420012008201520251980: 77 index1981: 62 index1982: 69 index1983: 66 index1984: 64 index1985: 62 index1986: 62 index1987: 62 index1988: 57 index1989: 57 index1990: 53 index1991: 50 index1992: 50 index1993: 51 index1994: 56 index1995: 52 index1996: 51 index1997: 52 index1998: 63 index1999: 58 index2000: 72 index2001: 71 index2002: 69 index2003: 65 index2004: 67 index2005: 67 index2006: 66 index2007: 73 index2008: 70 index2009: 63 index2010: 62 index2011: 62 index2012: 61 index2013: 58 index2014: 59 index2015: 57 index2016: 56 index2017: 55 index2018: 59 index2019: 58 index2020: 58 index2021: 59 index2022: 54 index2023: 57 index2024: 54 index2025: 53 index5060708019801996201220251980: 77 index1981: 62 index1982: 69 index1983: 66 index1984: 64 index1985: 62 index1986: 62 index1987: 62 index1988: 57 index1989: 57 index1990: 53 index1991: 50 index1992: 50 index1993: 51 index1994: 56 index1995: 52 index1996: 51 index1997: 52 index1998: 63 index1999: 58 index2000: 72 index2001: 71 index2002: 69 index2003: 65 index2004: 67 index2005: 67 index2006: 66 index2007: 73 index2008: 70 index2009: 63 index2010: 62 index2011: 62 index2012: 61 index2013: 58 index2014: 59 index2015: 57 index2016: 56 index2017: 55 index2018: 59 index2019: 58 index2020: 58 index2021: 59 index2022: 54 index2023: 57 index2024: 54 index2025: 53 index
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12, published 2026-07-13.
All 46 values
Periodindex
202553
202454
202357
202254
202159
202058
201958
201859
201755
201656
201557
201459
201358
201261
201162
201062
200963
200870
200773
200666
200567
200467
200365
200269
200171
200072
199958
199863
199752
199651
199552
199456
199351
199250
199150
199053
198957
198857
198762
198662
198562
198464
198366
198269
198162
198077

Cook County compared with nearby places

Adams County: 38 indexChampaign County: 43 indexClark County: 33 indexCook County: 53 indexDuPage County: 42 indexEffingham County: 35 indexHamilton County: 42 indexJersey County: 42 indexJo Daviess County: 33 indexKane County: 45 indexLake County: 39 indexMcHenry County: 42 indexMcLean County: 44 indexMacon County: 44 indexMacoupin County: 34 indexMadison County: 49 indexPeoria County: 45 indexRandolph County: 43 indexRock Island County: 41 indexSt. Clair County: 47 indexSangamon County: 41 indexWill County: 44 indexWinnebago County: 40 index
  • Under 38
  • 38 to 42
  • 42 to 43
  • 43 to 45
  • 45 and over
  • No data
Median Air Quality Index (US EPA), 2025, index. Cook County is outlined. Same source and period for every area shown. Source: U.S. Environmental Protection Agency. Boundaries: U.S. Census Bureau cartographic boundary files.

Rankings

Definition

Median of the daily Air Quality Index (AQI) values of a US county over the days of the year with an AQI, from the EPA AirData annual summaries.

More on how it is measured
  • The daily county AQI is the highest AQI among the monitors and pollutants reported that day (ozone, PM2.5, PM10, carbon monoxide and nitrogen dioxide).
  • Lower is cleaner: 0 to 50 is good, 51 to 100 moderate and above 100 unhealthy for sensitive groups.

United States counties with air quality monitors only, about 1,000 of some 3,100 in recent years; a county without monitors has no value. The number of days with an AQI differs between counties because some monitors run only in the ozone season.

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How to cite

U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.

Citation styles

The publisher is the author. Invokely is named only as the place the figures were read, where a style asks for it.

APA 7

U.S. Environmental Protection Agency. (2026). EPA AirData annual AQI by county: median daily AQI (Median Air Quality Index (US EPA), Cook County, 1980 to 2025) [Data set]. Retrieved October 12, 2026, from https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual

MLA 9

EPA AirData annual AQI by county: median daily AQI, Median Air Quality Index (US EPA), Cook County, 1980 to 2025. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/en/median-air-quality-index/cook-county-illinois. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: median daily AQI. Median Air Quality Index (US EPA), Cook County, 1980 to 2025. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/en/median-air-quality-index/cook-county-illinois.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: median daily AQI, Median Air Quality Index (US EPA), Cook County, 1980 to 2025 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/en/median-air-quality-index/cook-county-illinois (Accessed: 12 October 2026).

BibTeX
@misc{environmental_median_air_quality_index_2025,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: median daily AQI: Median Air Quality Index (US EPA), Cook County, 1980 to 2025}},
  year = {2026},
  howpublished = {Data set},
  url = {https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual},
  urldate = {2026-10-12},
  note = {Accessed via Invokely, https://invokely.ai/en/median-air-quality-index/cook-county-illinois. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download\_files.html\#Annual. Retrieved 2026-10-12.},
}
RIS
TY  - DATA
AU  - U.S. Environmental Protection Agency
TI  - EPA AirData annual AQI by county: median daily AQI: Median Air Quality Index (US EPA), Cook County, 1980 to 2025
PY  - 2026
DA  - 2026/07/13
PB  - U.S. Environmental Protection Agency
DB  - Invokely
UR  - https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual
L2  - https://invokely.ai/en/median-air-quality-index/cook-county-illinois
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/en/median-air-quality-index/cook-county-illinois.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
ER  -
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Questions

What is the median Air Quality Index (US EPA) in Cook County?

Median Air Quality Index (US EPA) in Cook County was 53 in 2025, according to the U.S. Environmental Protection Agency. That is down 1 from 2024. That is the 1st highest of 23 counties in 2025.

Where does this figure come from?

U.S. Environmental Protection Agency. EPA AirData annual AQI by county: median daily AQI. Retrieved by Invokely on 2026-10-12.

What was the highest median Air Quality Index (US EPA) in Cook County?

77 in 1980, the highest value since 1980 in this series.

Related statistics for Cook County

All statistics for Cook County | Cook County in figures