Median AQI
46
Good
South Dakota · County air quality · 2025
Custer County, South Dakota
Median AQI 46 (Good). 72.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 46
- Median AQI
- 72.4%
- Good-air days
- 0
- Unhealthy days
- 36%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Custer County's air is good on balance, more polluted than the median US county, a median AQI of 46 with 72.4% of 181 monitored days in the Good band, driven mainly by Ozone.
- 46
- median AQI · Good
- 72.4%
- days rated Good
- Ozone
- main pollutant
- 36%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 87.
Data updated July 2026
- Good · 131 d · 72.4%
- Moderate · 50 d · 27.6%
How did Custer County's air break down in 2025?
Across 181 monitored days, 131 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 87 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 181 days monitored. Median AQI: 46 (Good).
Insights: Custer County, South Dakota. EPA monitors recorded a median Air Quality Index of 46 across 181 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 131 (72%) fell in the Good band (AQI 0–50), 50 (28%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 61, while the worst single-day peak hit 87 (Moderate). Residents averaged about 21.7 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (128 days), PM2.5 (53 days). Across the 2020–2025 trend window, good days shifted by -192 and the median AQI moved +5 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 87, moderate but never Unhealthy. Nearby counties show comparable readings: Brookings (53.0% good, AQI 48); Brown (87.1% good, AQI 25); Clay (82.6% good, AQI 37); Codington (82.1% good, AQI 33); Hughes (94.4% good, AQI 14); Jackson (78.5% good, AQI 44).
Air Quality Summary
Good Days
72.4%
131 of 181 monitored days
-2.6pp vs 75% target
Max AQI Recorded
87
Moderate
Health Grade
Moderate
90th-pct AQI 61
Custer County, Good days share 72.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Custer 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 181 monitored days across EPA AQI categories.
Good
131
72%
Moderate
50
28%
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 Custer County.
- Ozone · 128 days · 70.7%
- PM2.5 · 53 days · 29.3%
Health Impact Assessment
Moderate
Custer County's air quality is rated Moderate based on 72.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 72.4% of monitored days in 2025, with a median AQI of 46. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 128 of 181 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Custer County. Best year: 2020 (323 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 323 | 41 | 2 | 0 | 41 | 119 |
| 2021 | 302 | 59 | 2 | 0 | 39 | 209 |
| 2022 | 298 | 62 | 2 | 0 | 41 | 130 |
| 2023 | 308 | 48 | 4 | 5 | 43 | 167 |
| 2024 | 276 | 81 | 9 | 0 | 44 | 126 |
| 2025 | 131 | 50 | 0 | 0 | 46 | 87 |
How does Custer County compare?
How Custer County compares
Good-day share worse than US avg
Custer County 72.4%
Brookings County, South Dakota 53.0%
US average 76.5%
Median AQI worse than US avg
Custer County 46
Brookings County, South Dakota 48
US average 38
Unhealthy days / yr about average
Custer County 0
Brookings County, South Dakota 1
US average 0
Other Counties in South Dakota
Air quality comparison for nearby counties in South Dakota.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Custer County.
Bay County, Florida
AQI 46 · 60.6% good
Blount County, Tennessee
AQI 46 · 69.6% good
Cache County, Utah
AQI 46 · 61.2% good
Chesterfield County, South Carolina
AQI 46 · 61.2% good
Clark County, Indiana
AQI 46 · 59.7% good
Clark County, Ohio
AQI 46 · 59.4% good
What Custer 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 46 means for exposure. Health guidance
- See how Custer County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Custer County with its South Dakota neighbours before drawing a conclusion about the region. All of South Dakota
Based on 181 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 Custer County, South Dakota? ▼
Custer County has a median Air Quality Index (AQI) of 46, rated "Good." 72.4% of monitored days (131 out of 181) had good air quality in 2025.
What is the main pollutant in Custer County? ▼
The primary pollutant in Custer County is Ozone (O3), which was the main AQI driver on 128 days (71% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Custer County have? ▼
In 2025, Custer County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 87.
Is the air quality in Custer County getting better or worse? ▼
Air quality in Custer County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 323 good days. Worst year: 2025 with 131 good days.
What does AQI 46 mean for health? ▼
Custer County's median AQI of 46 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 Custer County compare to other counties in South Dakota? ▼
Custer County has 72.4% good air days. Nearby counties in South Dakota: Brookings (53.0% good), Brown (87.1% good), Clay (82.6% good), Codington (82.1% good), Hughes (94.4% good), Jackson (78.5% good).
What is the 90th percentile AQI in Custer County? ▼
The 90th percentile AQI for Custer County is 61, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 87 (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.