Metro area air quality · 2025
Decatur, IL
Median AQI 44 (Good). 64.9% of monitored days rated Good across this metro's EPA monitoring network.
- 44
- Median AQI
- 64.9%
- Good-air days
- 0
- Unhealthy days
- 34%
- Cleaner than US metros
Decatur, IL posted a 2025 median AQI of 44 (Good) with 64.9% Good days
According to the U.S. EPA Air Quality System, the Decatur, IL CBSA recorded a median AQI of 44 across 365 monitored days in 2025, with 64.9% rated Good and 0 unhealthy or worse. This is an annual metro comparison, not a live advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US metros
- The Decatur, IL CBSA's 64.9% Good-day share places it cleaner than 34% of US metros in 2025.
- Closest median-AQI peer
- Bartlesville, OK (68.0% Good, median AQI 44) is the closest nationwide median-AQI peer to Decatur, IL.
- 2020–2025 Good-day shift
- Decatur, IL's Good-day share moved +6.4 points from 2020 to 2025 (median AQI -2).
- Median AQI
- Median AQI: 44
Aggregated from EPA Air Quality System (2025), 365 monitored days. EPA AQS →
The verdict
The Decatur, IL metro runs good on the EPA scale, more polluted than the median US metro, a median AQI of 44 with 64.9% of 365 monitored days in the Good band.
- 44
- median AQI · Good
- 64.9%
- days rated Good
- 34%
- cleaner than US metros
- 141
- worst single reading
No day crossed into the Unhealthy tier across the metro's monitors in 2025.
Annual release change
What changed in the 2025 EPA annual release
- Decatur, IL metro's peak single-day AQI rose from 101 to 141 between the 2024 and 2025 EPA annual releases, a change of +40 points.
Insights: Decatur, IL metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 44 over 365 measured days in 2025, which corresponds to a Good band and a Moderate metro-wide health grade. The monitored-day split lands at 237 Good days (65%), 125 Moderate (34%), and 3 Unhealthy-for-Sensitive-Groups (1%). The 90th-percentile AQI finished at 64 while the highest single-day reading hit 141 (USG). Metro residents averaged roughly 19.5 clean-air days per 30-day window across the reporting year.
Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +6.4 points and the median AQI moved -2 points, which classifies the multi-year trajectory as improving. The metro recorded no Unhealthy-tier days in this annual dataset. Metros with comparable AQI profiles include Bartlesville, OK (68.0% good, AQI 44); Berlin, NH-VT (81.5% good, AQI 44); Bloomington, IL (66.0% good, AQI 44).
Air Quality Summary
Median AQI
44
Good
Good Days
64.9%
237 of 365 days
Max AQI
141
USG
Health Grade
Moderate
90th pct: 64
AQI Day Breakdown (2025)
Distribution of 365 monitored days across EPA AQI categories.
Good
237
65%
Moderate
125
34%
USG
3
1%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Health Impact Assessment
The Decatur, IL metro area's air quality is rated Moderate based on 64.9% good air days. No unhealthy air days were recorded in 2025.
Air quality is generally acceptable. Unusually sensitive people should monitor real-time conditions at AirNow.gov during high-pollution events.
How does the Decatur, IL metro compare?
How Decatur, IL compares
5-Year Air Quality Trend
Air quality is improving in the Decatur, IL metro. Highest Good-day share: 2025 (65.5%, 237 of 362 monitored days).
| Year | Good | Moderate | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|
| 2020 | 214 | 148 | 0 | 46 | 90 |
| 2021 | 179 | 179 | 0 | 51 | 112 |
| 2022 | 209 | 154 | 0 | 46 | 115 |
| 2023 | 171 | 178 | 1 | 51 | 287 |
| 2024 | 238 | 127 | 0 | 43 | 101 |
| 2025 | 237 | 125 | 0 | 44 | 141 |
Metros with a similar median AQI
CBSA peers nationwide whose annual median AQI sits near Decatur, IL (44).
Bartlesville, OK
Median AQI 44 · 68.0% Good-day share
Berlin, NH-VT
Median AQI 44 · 81.5% Good-day share
Bloomington, IL
Median AQI 44 · 66.0% Good-day share
Boston-Cambridge-Newton, MA-NH
Median AQI 44 · 71.0% Good-day share
Bridgeport-Stamford-Norwalk, CT
Median AQI 44 · 64.7% Good-day share
Buffalo-Cheektowaga-Niagara Falls, NY
Median AQI 44 · 63.8% Good-day share
Metros with similar unhealthy-day exposure
A second relationship type: metros whose unhealthy-or-worse day count is closest to Decatur, IL's 0 (independent of median AQI).
Aberdeen, SD
0 unhealthy-or-worse days · median AQI 27
Aberdeen, WA
0 unhealthy-or-worse days · median AQI 22
Adrian, MI
0 unhealthy-or-worse days · median AQI 41
Akron, OH
0 unhealthy-or-worse days · median AQI 45
Albany, GA
0 unhealthy-or-worse days · median AQI 46
Albany, OR
0 unhealthy-or-worse days · median AQI 27
More Air Quality Data
Explore EPA air quality rankings and guides across U.S. metros and counties.
Cleanest Metro Areas
U.S. metros ranked by their share of Good air-quality days.
Worst Air Quality
Counties and metros with the most unhealthy air days.
All Metro Areas
Annual AQI by CBSA for every monitored U.S. metro area.
Best and Worst City Air
What drives urban air quality and how metro areas compare.
Air Quality Guides
Frequently Asked Questions
What is the air quality in the Decatur, IL metro area? ▼
How many unhealthy air days does Decatur, IL have? ▼
Is air quality in Decatur, IL getting better or worse? ▼
What does AQI 44 mean for health? ▼
What is the 90th percentile AQI for Decatur, IL? ▼
How does Decatur, IL compare to other metro areas? ▼
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by CBSA dataset, 2020–2025. See our methodology for how AQI, median, and coverage figures are computed.
Read our methodology , how this data is sourced, computed, and verified.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by CBSA summary files (metro-level) · 2020–2025
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Every figure on PlainAirData 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.