EnviroNearby

Sangamon County, Illinois air quality history

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

70%
Good days in 2025
41
Median daily AQI, 2025
3
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 Sangamon, Illinois on 365 days. 256 of those days (70%) were in the Good range, and the median daily AQI was 41. That median is about the same as the typical monitored county in Illinois (median 42 across 23 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 217 days. Across the years with fuller monitoring, the share of Good days fell: an average of 70% in 1980–1982 versus 64% 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 213 of 351 days1980: Moderate 118 of 351 days1980: Unhealthy for Sensitive Groups 19 of 351 days1980: Unhealthy 1 of 351 days19801981: Good 273 of 357 days1981: Moderate 77 of 357 days1981: Unhealthy for Sensitive Groups 6 of 357 days1981: Unhealthy 1 of 357 days1982: Good 261 of 362 days1982: Moderate 91 of 362 days1982: Unhealthy for Sensitive Groups 9 of 362 days1982: Unhealthy 1 of 362 days1983: Good 244 of 364 days1983: Moderate 84 of 364 days1983: Unhealthy for Sensitive Groups 33 of 364 days1983: Unhealthy 3 of 364 days1984: Good 277 of 365 days1984: Moderate 69 of 365 days1984: Unhealthy for Sensitive Groups 16 of 365 days1984: Unhealthy 3 of 365 days1985: Good 282 of 362 days1985: Moderate 70 of 362 days1985: Unhealthy for Sensitive Groups 8 of 362 days1985: Unhealthy 2 of 362 days19851986: Good 279 of 352 days1986: Moderate 58 of 352 days1986: Unhealthy for Sensitive Groups 12 of 352 days1986: Unhealthy 2 of 352 days1986: Very Unhealthy 1 of 352 days1987: Good 261 of 361 days1987: Moderate 73 of 361 days1987: Unhealthy for Sensitive Groups 25 of 361 days1987: Unhealthy 2 of 361 days1988: Good 263 of 359 days1988: Moderate 54 of 359 days1988: Unhealthy for Sensitive Groups 27 of 359 days1988: Unhealthy 15 of 359 days1989: Good 287 of 364 days1989: Moderate 63 of 364 days1989: Unhealthy for Sensitive Groups 12 of 364 days1989: Unhealthy 2 of 364 days1990: Good 322 of 364 days1990: Moderate 33 of 364 days1990: Unhealthy for Sensitive Groups 9 of 364 days19901991: Good 297 of 365 days1991: Moderate 52 of 365 days1991: Unhealthy for Sensitive Groups 13 of 365 days1991: Unhealthy 2 of 365 days1991: Very Unhealthy 1 of 365 days1992: Good 319 of 366 days1992: Moderate 39 of 366 days1992: Unhealthy for Sensitive Groups 7 of 366 days1992: Unhealthy 1 of 366 days1993: Good 319 of 365 days1993: Moderate 36 of 365 days1993: Unhealthy for Sensitive Groups 9 of 365 days1993: Unhealthy 1 of 365 days1994: Good 298 of 365 days1994: Moderate 49 of 365 days1994: Unhealthy for Sensitive Groups 15 of 365 days1994: Unhealthy 3 of 365 days1995: Good 309 of 365 days1995: Moderate 40 of 365 days1995: Unhealthy for Sensitive Groups 14 of 365 days1995: Unhealthy 2 of 365 days19951996: Good 311 of 366 days1996: Moderate 46 of 366 days1996: Unhealthy for Sensitive Groups 7 of 366 days1996: Unhealthy 2 of 366 days1997: Good 326 of 365 days1997: Moderate 35 of 365 days1997: Unhealthy for Sensitive Groups 4 of 365 days1998: Good 308 of 365 days1998: Moderate 44 of 365 days1998: Unhealthy for Sensitive Groups 13 of 365 days1999: Good 272 of 365 days1999: Moderate 85 of 365 days1999: Unhealthy for Sensitive Groups 6 of 365 days1999: Unhealthy 2 of 365 days2000: Good 253 of 366 days2000: Moderate 105 of 366 days2000: Unhealthy for Sensitive Groups 7 of 366 days2000: Unhealthy 1 of 366 days20002001: Good 249 of 365 days2001: Moderate 109 of 365 days2001: Unhealthy for Sensitive Groups 6 of 365 days2001: Unhealthy 1 of 365 days2002: Good 253 of 365 days2002: Moderate 99 of 365 days2002: Unhealthy for Sensitive Groups 13 of 365 days2003: Good 256 of 365 days2003: Moderate 101 of 365 days2003: Unhealthy for Sensitive Groups 8 of 365 days2004: Good 270 of 366 days2004: Moderate 94 of 366 days2004: Unhealthy for Sensitive Groups 2 of 366 days2005: Good 255 of 365 days2005: Moderate 95 of 365 days2005: Unhealthy for Sensitive Groups 15 of 365 days20052006: Good 298 of 365 days2006: Moderate 66 of 365 days2006: Unhealthy for Sensitive Groups 1 of 365 days2007: Good 277 of 365 days2007: Moderate 83 of 365 days2007: Unhealthy for Sensitive Groups 5 of 365 days2008: Good 297 of 366 days2008: Moderate 69 of 366 days2009: Good 293 of 365 days2009: Moderate 72 of 365 days2010: Good 272 of 365 days2010: Moderate 92 of 365 days2010: Unhealthy for Sensitive Groups 1 of 365 days20102011: Good 308 of 365 days2011: Moderate 53 of 365 days2011: Unhealthy for Sensitive Groups 3 of 365 days2011: Unhealthy 1 of 365 days2012: Good 286 of 366 days2012: Moderate 67 of 366 days2012: Unhealthy for Sensitive Groups 13 of 366 days2013: Good 326 of 365 days2013: Moderate 39 of 365 days2014: Good 319 of 358 days2014: Moderate 39 of 358 days2015: Good 292 of 349 days2015: Moderate 57 of 349 days20152016: Good 304 of 364 days2016: Moderate 59 of 364 days2016: Unhealthy for Sensitive Groups 1 of 364 days2017: Good 262 of 364 days2017: Moderate 100 of 364 days2017: Unhealthy for Sensitive Groups 2 of 364 days2018: Good 189 of 363 days2018: Moderate 173 of 363 days2018: Unhealthy for Sensitive Groups 1 of 363 days2019: Good 222 of 360 days2019: Moderate 138 of 360 days2020: Good 254 of 364 days2020: Moderate 110 of 364 days20202021: Good 233 of 362 days2021: Moderate 129 of 362 days2022: Good 220 of 362 days2022: Moderate 138 of 362 days2022: Unhealthy for Sensitive Groups 4 of 362 days2023: Good 182 of 365 days2023: Moderate 163 of 365 days2023: Unhealthy for Sensitive Groups 17 of 365 days2023: Unhealthy 2 of 365 days2023: Very Unhealthy 1 of 365 days2024: Good 263 of 366 days2024: Moderate 102 of 366 days2024: Unhealthy for Sensitive Groups 1 of 366 days2025: Good 256 of 365 days2025: Moderate 106 of 365 days2025: Unhealthy for Sensitive Groups 3 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 881981: 90th percentile AQI 671982: 90th percentile AQI 781983: 90th percentile AQI 1001984: 90th percentile AQI 841985: 90th percentile AQI 711986: 90th percentile AQI 771987: 90th percentile AQI 901988: 90th percentile AQI 1081989: 90th percentile AQI 771990: 90th percentile AQI 581991: 90th percentile AQI 771992: 90th percentile AQI 541993: 90th percentile AQI 541994: 90th percentile AQI 711995: 90th percentile AQI 711996: 90th percentile AQI 611997: 90th percentile AQI 541998: 90th percentile AQI 641999: 90th percentile AQI 772000: 90th percentile AQI 712001: 90th percentile AQI 742002: 90th percentile AQI 752003: 90th percentile AQI 732004: 90th percentile AQI 642005: 90th percentile AQI 842006: 90th percentile AQI 592007: 90th percentile AQI 642008: 90th percentile AQI 592009: 90th percentile AQI 602010: 90th percentile AQI 652011: 90th percentile AQI 642012: 90th percentile AQI 772013: 90th percentile AQI 512014: 90th percentile AQI 512015: 90th percentile AQI 552016: 90th percentile AQI 572017: 90th percentile AQI 622018: 90th percentile AQI 662019: 90th percentile AQI 612020: 90th percentile AQI 582021: 90th percentile AQI 622022: 90th percentile AQI 622023: 90th percentile AQI 742024: 90th percentile AQI 582025: 90th percentile AQI 611980: Median AQI 441981: Median AQI 391982: Median AQI 421983: Median AQI 431984: Median AQI 411985: Median AQI 401986: Median AQI 371987: Median AQI 351988: Median AQI 351989: Median AQI 381990: Median AQI 321991: Median AQI 361992: Median AQI 321993: Median AQI 341994: Median AQI 341995: Median AQI 331996: Median AQI 331997: Median AQI 311998: Median AQI 321999: Median AQI 372000: Median AQI 392001: Median AQI 392002: Median AQI 402003: Median AQI 392004: Median AQI 382005: Median AQI 392006: Median AQI 342007: Median AQI 362008: Median AQI 362009: Median AQI 332010: Median AQI 402011: Median AQI 322012: Median AQI 372013: Median AQI 352014: Median AQI 332015: Median AQI 352016: Median AQI 362017: Median AQI 432018: Median AQI 492019: Median AQI 452020: Median AQI 442021: Median AQI 432022: Median AQI 452023: Median AQI 512024: Median AQI 412025: Median AQI 411980198519901995200020052010201520202025
  • 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)21759%
Ozone14841%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202536525610630004161142PM2.5
202436626310210004158105PM2.5
2023365182163172105174247PM2.5
202236222013840004562126PM2.5
20213622331290000436298PM2.5
20203642541100000445897PM2.5
20193602221380000456187PM2.5
201836318917310004966122PM2.5
201736426210020004362115Ozone
20163643045910003657105Ozone
2015349292570000355587Ozone
2014358319390000335180Ozone
20133653263900003551100Ozone
201236628667130003777136Ozone
20113653085331003264154Ozone
20103652729210004065105Ozone
2009365293720000336080Ozone
2008366297690000365990Ozone
20073652778350003664136Ozone
20063652986610003459112Ozone
200536525595150003984126Ozone
20043662709420003864102Ozone
200336525610180003973133Ozone
200236525399130004075147Ozone
200136524910961003974174Ozone
200036625310571003971164Ozone
19993652728562003777164Ozone
199836530844130003264140Ozone
19973653263540003154119Ozone
19963663114672003361151Ozone
199536530940142003371172Ozone
199436529849153003471169Ozone
19933653193691003454164Ozone
19923663193971003254151Ozone
199136529752132103677216Ozone
19903643223390003258150Ozone
198936428763122003877169Ozone
19883592635427150035108195Ozone
198736126173252003590166Ozone
198635227958122103777201Ozone
19853622827082004071182Ozone
198436527769163004184166Ozone
1983364244843330043100166Ozone
19823622619191004278169Ozone
19813572737761003967172CO
1980351213118191004488151CO

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