EnviroNearby

Will County, Illinois air quality history

Daily Air Quality Index summaries from EPA monitors in Will, Illinois, 1980–2025.

62%
Good days in 2025
44
Median daily AQI, 2025
5
Days above 100 in 2025
365
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Will, Illinois on 365 days. 225 of those days (62%) were in the Good range, and the median daily AQI was 44. That median is about the same as the typical monitored county in Illinois (median 42 across 23 counties), and higher than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 241 days. Across the years with fuller monitoring, the share of Good days fell: an average of 77% in 1980–1982 versus 57% in 2023–2025.

How the days broke down each year

Each bar is one year. The colored segments show the share of monitored days that fell in each AQI category.

Share of monitored days in each AQI category, by year0%25%50%75%100%1980: Good 262 of 357 days1980: Moderate 75 of 357 days1980: Unhealthy for Sensitive Groups 17 of 357 days1980: Unhealthy 3 of 357 days19801981: Good 273 of 360 days1981: Moderate 74 of 360 days1981: Unhealthy for Sensitive Groups 10 of 360 days1981: Unhealthy 3 of 360 days1982: Good 294 of 362 days1982: Moderate 54 of 362 days1982: Unhealthy for Sensitive Groups 13 of 362 days1982: Very Unhealthy 1 of 362 days1983: Good 287 of 365 days1983: Moderate 51 of 365 days1983: Unhealthy for Sensitive Groups 19 of 365 days1983: Unhealthy 6 of 365 days1983: Very Unhealthy 2 of 365 days1984: Good 295 of 366 days1984: Moderate 53 of 366 days1984: Unhealthy for Sensitive Groups 18 of 366 days1985: Good 287 of 365 days1985: Moderate 65 of 365 days1985: Unhealthy for Sensitive Groups 12 of 365 days1985: Unhealthy 1 of 365 days19851986: Good 303 of 365 days1986: Moderate 56 of 365 days1986: Unhealthy for Sensitive Groups 6 of 365 days1987: Good 291 of 361 days1987: Moderate 50 of 361 days1987: Unhealthy for Sensitive Groups 16 of 361 days1987: Unhealthy 4 of 361 days1988: Good 196 of 304 days1988: Moderate 56 of 304 days1988: Unhealthy for Sensitive Groups 34 of 304 days1988: Unhealthy 18 of 304 days1989: Good 286 of 364 days1989: Moderate 59 of 364 days1989: Unhealthy for Sensitive Groups 17 of 364 days1989: Unhealthy 2 of 364 days1990: Good 307 of 355 days1990: Moderate 44 of 355 days1990: Unhealthy for Sensitive Groups 4 of 355 days19901991: Good 299 of 363 days1991: Moderate 52 of 363 days1991: Unhealthy for Sensitive Groups 9 of 363 days1991: Unhealthy 2 of 363 days1991: Very Unhealthy 1 of 363 days1992: Good 323 of 364 days1992: Moderate 35 of 364 days1992: Unhealthy for Sensitive Groups 4 of 364 days1992: Unhealthy 2 of 364 days1993: Good 329 of 364 days1993: Moderate 31 of 364 days1993: Unhealthy for Sensitive Groups 4 of 364 days1994: Good 315 of 364 days1994: Moderate 43 of 364 days1994: Unhealthy for Sensitive Groups 5 of 364 days1994: Unhealthy 1 of 364 days1995: Good 304 of 363 days1995: Moderate 38 of 363 days1995: Unhealthy for Sensitive Groups 15 of 363 days1995: Unhealthy 6 of 363 days19951996: Good 300 of 366 days1996: Moderate 52 of 366 days1996: Unhealthy for Sensitive Groups 14 of 366 days1997: Good 309 of 365 days1997: Moderate 47 of 365 days1997: Unhealthy for Sensitive Groups 8 of 365 days1997: Unhealthy 1 of 365 days1998: Good 277 of 365 days1998: Moderate 74 of 365 days1998: Unhealthy for Sensitive Groups 11 of 365 days1998: Unhealthy 3 of 365 days1999: Good 251 of 365 days1999: Moderate 92 of 365 days1999: Unhealthy for Sensitive Groups 19 of 365 days1999: Unhealthy 3 of 365 days2000: Good 232 of 366 days2000: Moderate 127 of 366 days2000: Unhealthy for Sensitive Groups 6 of 366 days2000: Unhealthy 1 of 366 days20002001: Good 220 of 364 days2001: Moderate 124 of 364 days2001: Unhealthy for Sensitive Groups 19 of 364 days2001: Unhealthy 1 of 364 days2002: Good 216 of 365 days2002: Moderate 121 of 365 days2002: Unhealthy for Sensitive Groups 20 of 365 days2002: Unhealthy 8 of 365 days2003: Good 263 of 364 days2003: Moderate 87 of 364 days2003: Unhealthy for Sensitive Groups 13 of 364 days2003: Unhealthy 1 of 364 days2004: Good 273 of 340 days2004: Moderate 64 of 340 days2004: Unhealthy for Sensitive Groups 3 of 340 days2005: Good 209 of 321 days2005: Moderate 100 of 321 days2005: Unhealthy for Sensitive Groups 12 of 321 days20052006: Good 284 of 359 days2006: Moderate 73 of 359 days2006: Unhealthy for Sensitive Groups 2 of 359 days2007: Good 284 of 362 days2007: Moderate 71 of 362 days2007: Unhealthy for Sensitive Groups 7 of 362 days2008: Good 314 of 361 days2008: Moderate 47 of 361 days2009: Good 315 of 365 days2009: Moderate 50 of 365 days2010: Good 292 of 351 days2010: Moderate 57 of 351 days2010: Unhealthy for Sensitive Groups 2 of 351 days20102011: Good 334 of 359 days2011: Moderate 23 of 359 days2011: Unhealthy for Sensitive Groups 1 of 359 days2011: Unhealthy 1 of 359 days2012: Good 303 of 359 days2012: Moderate 52 of 359 days2012: Unhealthy for Sensitive Groups 4 of 359 days2013: Good 271 of 365 days2013: Moderate 94 of 365 days2014: Good 171 of 362 days2014: Moderate 191 of 362 days2015: Good 153 of 364 days2015: Moderate 211 of 364 days20152016: Good 201 of 365 days2016: Moderate 163 of 365 days2016: Unhealthy for Sensitive Groups 1 of 365 days2017: Good 231 of 365 days2017: Moderate 134 of 365 days2018: Good 194 of 365 days2018: Moderate 167 of 365 days2018: Unhealthy for Sensitive Groups 4 of 365 days2019: Good 179 of 365 days2019: Moderate 186 of 365 days2020: Good 183 of 363 days2020: Moderate 176 of 363 days2020: Unhealthy for Sensitive Groups 3 of 363 days2020: Unhealthy 1 of 363 days20202021: Good 157 of 365 days2021: Moderate 206 of 365 days2021: Unhealthy for Sensitive Groups 2 of 365 days2022: Good 193 of 365 days2022: Moderate 170 of 365 days2022: Unhealthy for Sensitive Groups 2 of 365 days2023: Good 155 of 365 days2023: Moderate 191 of 365 days2023: Unhealthy for Sensitive Groups 14 of 365 days2023: Unhealthy 3 of 365 days2023: Very Unhealthy 2 of 365 days2024: Good 245 of 365 days2024: Moderate 120 of 365 days2025: Good 225 of 365 days2025: Moderate 135 of 365 days2025: Unhealthy for Sensitive Groups 4 of 365 days2025: Unhealthy 1 of 365 days2025
  • Good
  • Moderate
  • Unhealthy for Sensitive Groups
  • Unhealthy
  • Very Unhealthy
  • Hazardous

Typical and high-end AQI over time

The median is the middle day of the year. The 90th percentile is the level that only the highest 10% of days exceeded.

Median and 90th-percentile daily AQI, by year0501001501980: 90th percentile AQI 891981: 90th percentile AQI 721982: 90th percentile AQI 741983: 90th percentile AQI 871984: 90th percentile AQI 801985: 90th percentile AQI 801986: 90th percentile AQI 581987: 90th percentile AQI 771988: 90th percentile AQI 1291989: 90th percentile AQI 771990: 90th percentile AQI 581991: 90th percentile AQI 671992: 90th percentile AQI 521993: 90th percentile AQI 501994: 90th percentile AQI 611995: 90th percentile AQI 741996: 90th percentile AQI 771997: 90th percentile AQI 641998: 90th percentile AQI 771999: 90th percentile AQI 842000: 90th percentile AQI 792001: 90th percentile AQI 872002: 90th percentile AQI 932003: 90th percentile AQI 712004: 90th percentile AQI 632005: 90th percentile AQI 842006: 90th percentile AQI 622007: 90th percentile AQI 672008: 90th percentile AQI 542009: 90th percentile AQI 542010: 90th percentile AQI 612011: 90th percentile AQI 472012: 90th percentile AQI 612013: 90th percentile AQI 582014: 90th percentile AQI 672015: 90th percentile AQI 662016: 90th percentile AQI 622017: 90th percentile AQI 622018: 90th percentile AQI 702019: 90th percentile AQI 662020: 90th percentile AQI 642021: 90th percentile AQI 672022: 90th percentile AQI 662023: 90th percentile AQI 782024: 90th percentile AQI 602025: 90th percentile AQI 711980: Median AQI 361981: Median AQI 391982: Median AQI 351983: Median AQI 361984: Median AQI 341985: Median AQI 351986: Median AQI 341987: Median AQI 311988: Median AQI 381989: Median AQI 331990: Median AQI 311991: Median AQI 311992: Median AQI 301993: Median AQI 321994: Median AQI 321995: Median AQI 311996: Median AQI 341997: Median AQI 331998: Median AQI 341999: Median AQI 412000: Median AQI 422001: Median AQI 442002: Median AQI 432003: Median AQI 372004: Median AQI 352005: Median AQI 422006: Median AQI 332007: Median AQI 362008: Median AQI 332009: Median AQI 332010: Median AQI 382011: Median AQI 332012: Median AQI 352013: Median AQI 412014: Median AQI 512015: Median AQI 532016: Median AQI 482017: Median AQI 452018: Median AQI 492019: Median AQI 512020: Median AQI 502021: Median AQI 522022: Median AQI 492023: Median AQI 532024: Median AQI 442025: Median AQI 441980198519901995200020052010201520202025
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 2025

On each monitored day, the AQI reflects whichever measured pollutant had the highest index. This counts how many days each pollutant set the AQI. A pollutant that was not measured here cannot appear.

PollutantDays as main pollutantShare of monitored days
Fine particles (PM2.5)24166%
Ozone12434%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202536522513541004471156PM2.5
20243652451200000446084PM2.5
2023365155191143205378246PM2.5
202236519317020004966101PM2.5
202136515720620005267105PM2.5
202036318317631005064156PM2.5
20193651791860000516684PM2.5
201836519416740004970126PM2.5
20173652311340000456293PM2.5
201636520116310004862105PM2.5
20153641532110000536693PM2.5
20143621711910000516797PM2.5
2013365271940000415891Ozone
20123593035240003561119Ozone
20113593342311003347164Ozone
20103512925720003861115Ozone
2009365315500000335497Ozone
2008361314470000335493Ozone
20073622847170003667122Ozone
20063592847320003362126Ozone
2005321209100120004284140Ozone
20043402736430003563119Ozone
200336426387131003771169Ozone
2002365216121208004393174Ozone
2001364220124191004487151Ozone
200036623212761004279151Ozone
199936525192193004184169Ozone
199836527774113003477159Ozone
19973653094781003364159Ozone
199636630052140003477147Ozone
199536330438156003174182Ozone
19943643154351003261190Ozone
19933643293140003250108Ozone
19923643233542003052166Ozone
19913632995292103167201Ozone
19903553074440003158122Ozone
198936428659172003377174Ozone
19883041965634180038129195Ozone
198736129150164003177200Ozone
19863653035660003458125Ozone
198536528765121003580164Ozone
198436629553180003480136Ozone
198336528751196203687210Ozone
198236229454130103574218Ozone
198136027374103003972179Ozone
198035726275173003689190Ozone

What this data can and can’t tell you

It is a county-level summary. EPA reports one AQI per day for the county, based on the monitors operating there. Air at a particular street, school or home can differ, especially near roads, industry or wildfire smoke.

It is not a health assessment. The AQI is EPA’s scale for communicating daily air quality. A county’s history can’t tell you what the health risk is for any particular person. For daily conditions and health guidance, see AirNow.

Rules change over time. EPA has revised AQI breakpoints, most recently for fine particles in 2024, so some year-to-year change can reflect the scale rather than the air.

Counties in Illinois with a similar median AQI in 2025

All monitored counties in Illinois

Source: U.S. EPA AirData, “Annual AQI by County” files for 1980–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem