Median AQI
42
Good
Wyoming · County air quality · 2025
Johnson County, Wyoming
Median AQI 42 (Good). 90.6% of monitored days rated Good, direct from EPA Air Quality System stations.
- 42
- Median AQI
- 90.6%
- Good-air days
- 0
- Unhealthy days
- 77%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Johnson County's air is good on balance, cleaner than most US counties, a median AQI of 42 with 90.6% of 180 monitored days in the Good band, driven mainly by Ozone.
- 42
- median AQI · Good
- 90.6%
- days rated Good
- Ozone
- main pollutant
- 77%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 84.
Data updated July 2026
- Good · 163 d · 90.6%
- Moderate · 17 d · 9.4%
How did Johnson County's air break down in 2025?
Across 180 monitored days, 163 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 84 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 180 days monitored. Median AQI: 42 (Good).
Insights: Johnson County, Wyoming. EPA monitors recorded a median Air Quality Index of 42 across 180 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 163 (91%) fell in the Good band (AQI 0–50), 17 (9%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 50, while the worst single-day peak hit 84 (Moderate). Residents averaged about 27.2 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (175 days), PM10 (4 days), NO2 (1 days). Across the 2020–2025 trend window, good days shifted by -174 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 84, moderate but never Unhealthy. Nearby counties show comparable readings: Albany (51.9% good, AQI 50); Campbell (77.3% good, AQI 43); Carbon (100.0% good, AQI 7); Converse (94.5% good, AQI 41); Fremont (61.3% good, AQI 48); Laramie (69.8% good, AQI 47).
Air Quality Summary
Good Days
90.6%
163 of 180 monitored days
15.6pp vs 75% target
Max AQI Recorded
84
Moderate
Health Grade
Excellent
90th-pct AQI 50
Johnson County, Good days share 90.6%
National avg
Share of monitored days at AQI 0-50 (Good band).
Johnson 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 180 monitored days across EPA AQI categories.
Good
163
91%
Moderate
17
9%
USG
0
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Johnson County.
- Ozone · 175 days · 97.2%
- PM10 · 4 days · 2.2%
- NO₂ · 1 days · 0.6%
Health Impact Assessment
Excellent
Johnson County's air quality is rated Excellent based on 90.6% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 90.6% 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 Ozone, driving AQI on 175 of 180 monitored days.
5-Year Air Quality Trend
Air quality is stable in Johnson County. Best year: 2023 (351 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 337 | 27 | 0 | 0 | 40 | 93 |
| 2021 | 304 | 54 | 7 | 0 | 40 | 126 |
| 2022 | 350 | 14 | 1 | 0 | 39 | 101 |
| 2023 | 351 | 13 | 0 | 0 | 40 | 64 |
| 2024 | 327 | 36 | 1 | 0 | 40 | 112 |
| 2025 | 163 | 17 | 0 | 0 | 42 | 84 |
How does Johnson County compare?
How Johnson County compares
Good-day share better than US avg
Johnson County 90.6%
Albany County, Wyoming 51.9%
US average 76.5%
Median AQI worse than US avg
Johnson County 42
Albany County, Wyoming 50
US average 38
Unhealthy days / yr about average
Johnson County 0
Albany County, Wyoming 0
US average 0
Other Counties in Wyoming
Air quality comparison for nearby counties in Wyoming.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Johnson 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 Johnson 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 42 means for exposure. Health guidance
- See how Johnson County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Johnson County with its Wyoming neighbours before drawing a conclusion about the region. All of Wyoming
Based on 180 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 Johnson County, Wyoming? ▼
Johnson County has a median Air Quality Index (AQI) of 42, rated "Good." 90.6% of monitored days (163 out of 180) had good air quality in 2025.
What is the main pollutant in Johnson County? ▼
The primary pollutant in Johnson County is Ozone (O3), which was the main AQI driver on 175 days (97% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Johnson County have? ▼
In 2025, Johnson County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 84.
Is the air quality in Johnson County getting better or worse? ▼
Air quality in Johnson County is stable based on 5-year trends (2020-2025). Best year: 2023 with 351 good days. Worst year: 2025 with 163 good days.
What does AQI 42 mean for health? ▼
Johnson 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 Johnson County compare to other counties in Wyoming? ▼
Johnson County has 90.6% good air days. Nearby counties in Wyoming: Albany (51.9% good), Campbell (77.3% good), Carbon (100.0% good), Converse (94.5% good), Fremont (61.3% good), Laramie (69.8% good).
What is the 90th percentile AQI in Johnson County? ▼
The 90th percentile AQI for Johnson County is 50, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 84 (Moderate).
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.