Median AQI
42
Good
Illinois · County air quality · 2025
Sangamon County, Illinois
Median AQI 42 (Good). 70.7% of monitored days rated Good, direct from EPA Air Quality System stations.
- 42
- Median AQI
- 70.7%
- Good-air days
- 0
- Unhealthy days
- 32%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Sangamon County's air is good on balance, more polluted than the median US county, a median AQI of 42 with 70.7% of 273 monitored days in the Good band, driven mainly by PM2.5.
- 42
- median AQI · Good
- 70.7%
- days rated Good
- PM2.5
- main pollutant
- 32%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 142.
Data updated July 2026
- Good · 193 d · 70.7%
- Moderate · 77 d · 28.2%
- USG · 3 d · 1.1%
How did Sangamon County's air break down in 2025?
Across 273 monitored days, 193 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 142 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 273 days monitored. Median AQI: 42 (Good).
Insights: Sangamon County, Illinois. EPA monitors recorded a median Air Quality Index of 42 across 273 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 193 (71%) fell in the Good band (AQI 0–50), 77 (28%) registered Moderate readings, and 3 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 61, while the worst single-day peak hit 142 (USG). Residents averaged about 21.2 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (142 days), Ozone (131 days). Across the 2020–2025 trend window, good days shifted by -61 and the median AQI moved -2 points, placing the multi-year trajectory at stable. The worst single reading over the 2020–2025 window was AQI 142, usg but never Unhealthy. Nearby counties show comparable readings: Adams (94.4% good, AQI 38); Champaign (63.7% good, AQI 44); Clark (92.1% good, AQI 36); Cook (40.5% good, AQI 53); DuPage (61.2% good, AQI 44); Effingham (95.7% good, AQI 35).
Air Quality Summary
Good Days
70.7%
193 of 273 monitored days
-4.3pp vs 75% target
Max AQI Recorded
142
USG
Health Grade
Moderate
90th-pct AQI 61
Sangamon County, Good days share 70.7%
National avg
Share of monitored days at AQI 0-50 (Good band).
Sangamon County, Unhealthy-or-worse share 0.0%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 273 monitored days across EPA AQI categories.
Good
193
71%
Moderate
77
28%
USG
3
1%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Sangamon County.
- PM2.5 · 142 days · 52.0%
- Ozone · 131 days · 48.0%
Health Impact Assessment
Moderate
Sangamon County's air quality is rated Moderate based on 70.7% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 70.7% of monitored days in 2025, with a median AQI of 42. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 142 of 273 monitored days.
5-Year Air Quality Trend
Air quality is stable in Sangamon County. Best year: 2024 (263 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 254 | 110 | 0 | 0 | 44 | 97 |
| 2021 | 233 | 129 | 0 | 0 | 43 | 98 |
| 2022 | 220 | 138 | 4 | 0 | 45 | 126 |
| 2023 | 182 | 163 | 17 | 2 | 51 | 247 |
| 2024 | 263 | 102 | 1 | 0 | 41 | 105 |
| 2025 | 193 | 77 | 3 | 0 | 42 | 142 |
How does Sangamon County compare?
How Sangamon County compares
Good-day share worse than US avg
Sangamon County 70.7%
Adams County, Illinois 94.4%
US average 76.5%
Median AQI worse than US avg
Sangamon County 42
Adams County, Illinois 38
US average 38
Unhealthy days / yr about average
Sangamon County 0
Adams County, Illinois 0
US average 0
Other Counties in Illinois
Air quality comparison for nearby counties in Illinois.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Sangamon County.
Adams County, Pennsylvania
AQI 42 · 73.8% good
Anderson County, Tennessee
AQI 42 · 91.0% good
Andrew County, Missouri
AQI 42 · 84.3% good
Armstrong County, Pennsylvania
AQI 42 · 68.1% good
Baldwin County, Alabama
AQI 42 · 72.2% good
Belmont County, Ohio
AQI 42 · 63.0% good
What Sangamon County's air means for you
The air here stays in the breathable range year-round, with PM2.5 the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 42 means for exposure. Health guidance
- See how Sangamon County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Sangamon County with its Illinois neighbours before drawing a conclusion about the region. All of Illinois
Based on 273 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in Sangamon County, Illinois? ▼
Sangamon County has a median Air Quality Index (AQI) of 42, rated "Good." 70.7% of monitored days (193 out of 273) had good air quality in 2025.
What is the main pollutant in Sangamon County? ▼
The primary pollutant in Sangamon County is Fine Particles (PM2.5), which was the main AQI driver on 142 days (52% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Sangamon County have? ▼
In 2025, Sangamon County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 142.
Is the air quality in Sangamon County getting better or worse? ▼
Air quality in Sangamon County is stable based on 5-year trends (2020-2025). Best year: 2024 with 263 good days. Worst year: 2023 with 182 good days.
What does AQI 42 mean for health? ▼
Sangamon County's median AQI of 42 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Sangamon County compare to other counties in Illinois? ▼
Sangamon County has 70.7% good air days. Nearby counties in Illinois: Adams (94.4% good), Champaign (63.7% good), Clark (92.1% good), Cook (40.5% good), DuPage (61.2% good), Effingham (95.7% good).
What is the 90th percentile AQI in Sangamon County? ▼
The 90th percentile AQI for Sangamon County is 61, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 142 (USG).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.