Median AQI
45
Good
Illinois · County air quality · 2025
Peoria County, Illinois
Median AQI 45 (Good). 59.9% of monitored days rated Good, direct from EPA Air Quality System stations.
- 45
- Median AQI
- 59.9%
- Good-air days
- 2
- Unhealthy days
- 15%
- Cleaner than US counties
Peoria County's 2025 annual median AQI is 45 (Good), with 59.9% Good days
According to the U.S. EPA Air Quality System, Peoria County, Illinois posted a 2025 median AQI of 45 (Good) across 357 monitored days, with 59.9% rated Good and 2 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Peoria County's 59.9% Good-day share places it cleaner than 15% of US counties in 2025.
- Closest median-AQI peer
- Baltimore County (64.7% Good, median AQI 45) is the closest nationwide median-AQI peer to Peoria County.
- 2020–2025 trend
- Peoria County's floor-qualifying Good-day share is worsening from 2020 to 2025 (67.9% → 59.9%).
- Median AQI
- Median AQI: 45
The verdict
According to EPA Air Quality System monitoring data, Peoria County's air is good on balance, among the more polluted 10% of US counties, a median AQI of 45 with 59.9% of 357 monitored days in the Good band, driven mainly by PM2.5.
- 45
- median AQI · Good
- 59.9%
- days rated Good
- PM2.5
- main pollutant
- 15%
- cleaner than US counties
2 days reached Unhealthy or worse; the worst single reading hit AQI 154.
Annual release change
What changed in the 2025 EPA annual release
- Peoria County's Good-day share fell from 68.6% to 59.9% between the 2024 and 2025 EPA annual releases, a change of -8.7 percentage points.
- Peoria County's peak single-day AQI rose from 100 to 154 between the 2024 and 2025 EPA annual releases, a change of +54 points.
- Peoria County's Unhealthy-category days rose from 0 to 2 between the 2024 and 2025 EPA annual releases, a change of +2 days.
Data updated August 2026
- Good · 214 d · 59.9%
- Moderate · 139 d · 38.9%
- USG · 2 d · 0.6%
- Unhealthy · 2 d · 0.6%
How did Peoria County's air break down in 2025?
Across 357 monitored days, 214 fell in the Good band (AQI 0–50) and 2 reached Unhealthy or worse. The worst single day peaked at AQI 154 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 357 days monitored. Median AQI: 45 (Good).
Insights: Peoria County, Illinois. EPA monitors recorded a median Air Quality Index of 45 across 357 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 214 (60%) fell in the Good band (AQI 0–50), 139 (39%) registered Moderate readings, and 2 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 66, while the worst single-day peak hit 154 (Unhealthy). Residents averaged about 18.0 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (235 days), Ozone (122 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by -7.9 points and the median AQI moved +1 points, placing the multi-year trajectory at worsening. The annual record contains 2 days at Unhealthy or worse. On those days, the EPA recommends that sensitive groups limit prolonged outdoor exertion. Nearby counties show comparable readings: Adams (94.7% good, AQI 38); Champaign (65.8% good, AQI 43); Clark (93.8% good, AQI 33); Cook (40.8% good, AQI 53); DuPage (63.8% good, AQI 42); Effingham (95.5% good, AQI 35).
Air Quality Summary
Good Days
59.9%
214 of 357 monitored days
-15.1pp vs 75% target
Max AQI Recorded
154
Unhealthy
Health Grade
Moderate
90th-pct AQI 66
Peoria County, Good days share 59.9%
National avg
Share of monitored days at AQI 0-50 (Good band).
Peoria County, Unhealthy-or-worse share 5.6%
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 357 monitored days across EPA AQI categories.
Good
214
60%
Moderate
139
39%
USG
2
1%
Unhealthy
2
1%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Peoria County.
- PM2.5 · 235 days · 65.8%
- Ozone · 122 days · 34.2%
Health Impact Assessment
Moderate
Peoria County's air quality is rated Moderate based on 59.9% good air days. There were 2 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 2 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 154. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is PM2.5, driving AQI on 235 of 357 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Peoria County. Highest Good-day share: 2024 (68.6%, 236 of 344 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 247 | 116 | 1 | 0 | 44 | 115 |
| 2021 | 181 | 179 | 1 | 0 | 50 | 101 |
| 2022 | 181 | 138 | 0 | 0 | 48 | 100 |
| 2023 | 187 | 131 | 21 | 1 | 48 | 151 |
| 2024 | 236 | 108 | 0 | 0 | 44 | 100 |
| 2025 | 214 | 139 | 2 | 2 | 45 | 154 |
How does Peoria County compare?
How Peoria County compares
Good-day share worse than typical
Peoria County 59.9%
Baltimore County, Maryland 64.7%
Typical US county 76.0%
Median AQI worse than typical
Peoria County 45
Baltimore County, Maryland 45
Typical US county 39
Unhealthy days / yr worse than typical
Peoria County 2
Baltimore County, Maryland 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Peoria County (45), not geographic neighbors.
Baltimore County, Maryland
Median AQI 45 · 64.7% Good-day share
Bell County, Texas
Median AQI 45 · 66.0% Good-day share
Box Elder County, Utah
Median AQI 45 · 64.7% Good-day share
Bronx County, New York
Median AQI 45 · 59.2% Good-day share
Catano County, Puerto Rico
Median AQI 45 · 60.6% Good-day share
Catron County, New Mexico
Median AQI 45 · 71.7% Good-day share
Same primary pollutant: PM2.5
PM2.5 led the AQI on the most monitored days here. These peers share that driver and the closest Good-day share (a second relationship type beyond median-AQI neighbors).
Allen County, Indiana
60.0% Good-day share · median AQI 44
Holmes County, Florida
60.0% Good-day share · median AQI 46
San Joaquin County, California
60.0% Good-day share · median AQI 46
Vigo County, Indiana
59.7% Good-day share · median AQI 45
Orange County, Texas
60.2% Good-day share · median AQI 45
Hamilton County, Florida
60.2% Good-day share · median AQI 46
Illinois counties on the map
Geographic containment only, other monitored counties in Illinois, independent of AQI or pollutant match.
What Peoria County's air means for you
On most days the air here is fine, but PM2.5 drives 2 unhealthy-or-worse days a year that sensitive groups should plan around.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 45 means for exposure. Health guidance
- See how Peoria County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Peoria County with its Illinois neighbours before drawing a conclusion about the region. All of Illinois
Based on 357 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
Keep exploring the annual AQI record
Air-quality reading list
Frequently Asked Questions
What is the air quality in Peoria County, Illinois? ▼
Peoria County has a median Air Quality Index (AQI) of 45, rated "Good." 59.9% of monitored days (214 out of 357) had good air quality in 2025.
What is the main pollutant in Peoria County? ▼
The primary pollutant in Peoria County is Fine Particles (PM2.5), which was the main AQI driver on 235 days (66% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Peoria County have? ▼
In 2025, Peoria County recorded 2 unhealthy air days (2 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 154.
Is the air quality in Peoria County getting better or worse? ▼
Air quality in Peoria County is worsening across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2024 at 68.6% (236 of 344 days). Lowest qualifying Good-day share: 2021 at 50.1% (181 of 361 days).
What does AQI 45 mean for health? ▼
Peoria County's median AQI of 45 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Peoria County compare to other counties in Illinois? ▼
Peoria County has 59.9% good air days. Nearby counties in Illinois: Adams (94.7% good), Champaign (65.8% good), Clark (93.8% good), Cook (40.8% good), DuPage (63.8% good), Effingham (95.5% good).
What is the 90th percentile AQI in Peoria County? ▼
The 90th percentile AQI for Peoria County is 66, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 154 (Unhealthy).
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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Peoria County, Illinois · 2020–2025
Share this annual record
Send the source-year summary or download its ready-to-use data card.
Download this county's annual AQI row as CSV , with the same EPA fields and denominator shown on this page.
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.