Median AQI
44
Good
Indiana · County air quality · 2025
Porter County, Indiana
Median AQI 44 (Good). 61.9% of monitored days rated Good, direct from EPA Air Quality System stations.
- 44
- Median AQI
- 61.9%
- Good-air days
- 0
- Unhealthy days
- 17%
- Cleaner than US counties
Porter County's 2025 annual median AQI is 44 (Good), with 61.9% Good days
According to the U.S. EPA Air Quality System, Porter County, Indiana posted a 2025 median AQI of 44 (Good) across 365 monitored days, with 61.9% rated Good and 0 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Porter County's 61.9% Good-day share places it cleaner than 17% of US counties in 2025.
- Closest median-AQI peer
- Allegan County (63.9% Good, median AQI 44) is the closest nationwide median-AQI peer to Porter County.
- 2020–2025 trend
- Porter County's floor-qualifying Good-day share is worsening from 2020 to 2025 (67.5% → 61.9%).
- Median AQI
- Median AQI: 44
The verdict
According to EPA Air Quality System monitoring data, Porter County's air is good on balance, among the more polluted 10% of US counties, a median AQI of 44 with 61.9% of 365 monitored days in the Good band, driven mainly by Ozone.
- 44
- median AQI · Good
- 61.9%
- days rated Good
- Ozone
- main pollutant
- 17%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 136.
Annual release change
What changed in the 2025 EPA annual release
- Porter County's Good-day share fell from 66.4% to 61.9% between the 2024 and 2025 EPA annual releases, a change of -4.5 percentage points.
- Porter County's peak single-day AQI rose from 112 to 136 between the 2024 and 2025 EPA annual releases, a change of +24 points.
Data updated August 2026
- Good · 226 d · 61.9%
- Moderate · 128 d · 35.1%
- USG · 11 d · 3.0%
How did Porter County's air break down in 2025?
Across 365 monitored days, 226 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 136 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 365 days monitored. Median AQI: 44 (Good).
Insights: Porter County, Indiana. EPA monitors recorded a median Air Quality Index of 44 across 365 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 226 (62%) fell in the Good band (AQI 0–50), 128 (35%) registered Moderate readings, and 11 (3%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 71, while the worst single-day peak hit 136 (USG). Residents averaged about 18.6 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (189 days), PM2.5 (167 days), PM10 (9 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by -5.6 points and the median AQI moved +1 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 136, usg but never Unhealthy. Nearby counties show comparable readings: Allen (60.0% good, AQI 44); Bartholomew (72.6% good, AQI 43); Boone (89.7% good, AQI 35); Brown (95.9% good, AQI 34); Carroll (90.8% good, AQI 35); Clark (58.1% good, AQI 46).
Air Quality Summary
Good Days
61.9%
226 of 365 monitored days
-13.1pp vs 75% target
Max AQI Recorded
136
USG
Health Grade
Moderate
90th-pct AQI 71
Porter County, Good days share 61.9%
National avg
Share of monitored days at AQI 0-50 (Good band).
Porter 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 365 monitored days across EPA AQI categories.
Good
226
62%
Moderate
128
35%
USG
11
3%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Porter County.
- Ozone · 189 days · 51.8%
- PM2.5 · 167 days · 45.8%
- PM10 · 9 days · 2.5%
Health Impact Assessment
Moderate
Porter County's air quality is rated Moderate based on 61.9% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 61.9% of monitored days in 2025, with a median AQI of 44. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 189 of 365 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Porter County. Highest Good-day share: 2020 (67.5%, 247 of 366 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 247 | 113 | 5 | 1 | 43 | 151 |
| 2021 | 204 | 154 | 7 | 0 | 47 | 136 |
| 2022 | 229 | 130 | 5 | 0 | 46 | 202 |
| 2023 | 206 | 137 | 20 | 2 | 48 | 180 |
| 2024 | 243 | 121 | 2 | 0 | 44 | 112 |
| 2025 | 226 | 128 | 11 | 0 | 44 | 136 |
How does Porter County compare?
How Porter County compares
Good-day share worse than typical
Porter County 61.9%
Allegan County, Michigan 63.9%
Typical US county 76.0%
Median AQI worse than typical
Porter County 44
Allegan County, Michigan 44
Typical US county 39
Unhealthy days / yr better than typical
Porter County 0
Allegan County, Michigan 2
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Porter County (44), not geographic neighbors.
Allegan County, Michigan
Median AQI 44 · 63.9% Good-day share
Allen County, Indiana
Median AQI 44 · 60.0% Good-day share
Baker County, Florida
Median AQI 44 · 69.5% Good-day share
Bay County, Florida
Median AQI 44 · 66.4% Good-day share
Blount County, Tennessee
Median AQI 44 · 71.5% Good-day share
Cache County, Utah
Median AQI 44 · 66.0% Good-day share
Same primary pollutant: Ozone
Ozone 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).
Gila County, Arizona
62.7% Good-day share · median AQI 47
LaPorte County, Indiana
63.0% Good-day share · median AQI 43
La Plata County, Colorado
60.8% Good-day share · median AQI 48
Park County, Colorado
63.0% Good-day share · median AQI 48
Sutter County, California
63.2% Good-day share · median AQI 47
Davis County, Utah
63.3% Good-day share · median AQI 46
Indiana counties on the map
Geographic containment only, other monitored counties in Indiana, independent of AQI or pollutant match.
What Porter County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 44 means for exposure. Health guidance
- See how Porter County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Porter County with its Indiana neighbours before drawing a conclusion about the region. All of Indiana
Based on 365 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 Porter County, Indiana? ▼
Porter County has a median Air Quality Index (AQI) of 44, rated "Good." 61.9% of monitored days (226 out of 365) had good air quality in 2025.
What is the main pollutant in Porter County? ▼
The primary pollutant in Porter County is Ozone (O3), which was the main AQI driver on 189 days (52% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Porter County have? ▼
In 2025, Porter County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 136.
Is the air quality in Porter County getting better or worse? ▼
Air quality in Porter 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: 2020 at 67.5% (247 of 366 days). Lowest qualifying Good-day share: 2021 at 55.9% (204 of 365 days).
What does AQI 44 mean for health? ▼
Porter County's median AQI of 44 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Porter County compare to other counties in Indiana? ▼
Porter County has 61.9% good air days. Nearby counties in Indiana: Allen (60.0% good), Bartholomew (72.6% good), Boone (89.7% good), Brown (95.9% good), Carroll (90.8% good), Clark (58.1% good).
What is the 90th percentile AQI in Porter County? ▼
The 90th percentile AQI for Porter County is 71, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 136 (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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Porter County, Indiana · 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.