Montana · County air quality · 2025

Hill County, Montana

Median AQI 14 (Good). 92.1% of monitored days rated Good, direct from EPA Air Quality System stations.

14
Median AQI
92.1%
Good-air days
1
Unhealthy days
85%
Cleaner than US counties

Hill County's 2025 annual median AQI is 14 (Good), with 92.1% Good days

According to the U.S. EPA Air Quality System, Hill County, Montana posted a 2025 median AQI of 14 (Good) across 304 monitored days, with 92.1% rated Good and 1 unhealthy or worse. This is an annual comparison, not today's advisory.

Data source EPA Air Quality System (AQS)

Cleaner than US
Hill County's 92.1% Good-day share places it cleaner than 85% of US counties in 2025.
Closest median-AQI peer
Beaverhead County (94.7% Good, median AQI 13) is the closest nationwide median-AQI peer to Hill County.
2023–2025 trend
Hill County's floor-qualifying Good-day share is improving from 2023 to 2025 (79.8% → 92.1%).
Median AQI
Median AQI: 14

According to the 2025 EPA AQS county release on PlainAirData, Hill County, Montana ranks #18 of 951 by median AQI (14) and #143 by good-day share (92.1%). Ponce County, Puerto Rico is #1 of 951 by median AQI (3, 91.4% Good days) at good-day-share #159 ≠ largest of 7 at 100.0% Good days #1 by good-day share (100.0%, median AQI 9) at median-AQI #7.

Annual release change

What changed in the 2025 EPA annual release

2024 → 2025
  • Hill County's peak single-day AQI rose from 123 to 157 between the 2024 and 2025 EPA annual releases, a change of +34 points.
  • Hill County's Unhealthy-category days rose from 0 to 1 between the 2024 and 2025 EPA annual releases, a change of +1 days.

Compared against 339 monitored days in 2024 and 304 in 2025. These are arithmetic differences between two stored EPA annual summaries, not a cause claim or a live advisory.

National release changes Two-year CSV

Data updated August 2026

Hill County AQI category distribution Stacked-segment bar showing the share of monitored days that fell in each EPA AQI category, Good, Moderate, USG, Unhealthy, Very Unhealthy, Hazardous, with median AQI marker. AQI category distribution 304 monitored days G Median AQI 14 0 50 100 150 200 300 500 Hill County
  • Good · 280 d · 92.1%
  • Moderate · 22 d · 7.2%
  • USG · 1 d · 0.3%
  • Unhealthy · 1 d · 0.3%

How did Hill County's air break down in 2025?

Across 304 monitored days, 280 fell in the Good band (AQI 0–50) and 1 reached Unhealthy or worse. The worst single day peaked at AQI 157 (Unhealthy).

EPA AQS →
Hill County, Good days share 92.1%
National avg

Share of monitored days at AQI 0-50 (Good band).

Hill County, Unhealthy-or-worse share 3.3%
National avg

Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).

Where Hill County sits nationally

COUNT-derived placement among 951 US counties with at least 100 monitored days in 2025. Hill County's Good-day share is 92.1% - cleaner than 85% of that comparison set.

Hill County Good-day share vs. every US county

Share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release

92.1% Cleaner than 85% higher than 85% of 951 US counties

0.0%–5.0%: 0 US counties (0%). Below this entry. 5.0%–10.0%: 1 US counties (0%). Below this entry. 10.0%–15.0%: 4 US counties (0%). Below this entry. 15.0%–20.0%: 4 US counties (0%). Below this entry. 20.0%–25.0%: 1 US counties (0%). Below this entry. 25.0%–30.0%: 5 US counties (1%). Below this entry. 30.0%–35.0%: 9 US counties (1%). Below this entry. 35.0%–40.0%: 4 US counties (0%). Below this entry. 40.0%–45.0%: 16 US counties (2%). Below this entry. 45.0%–50.0%: 16 US counties (2%). Below this entry. 50.0%–55.0%: 32 US counties (3%). Below this entry. 55.0%–60.0%: 50 US counties (5%). Below this entry. 60.0%–65.0%: 77 US counties (8%). Below this entry. 65.0%–70.0%: 93 US counties (10%). Below this entry. 70.0%–75.0%: 109 US counties (11%). Below this entry. 75.0%–80.0%: 114 US counties (12%). Below this entry. 80.0%–85.0%: 123 US counties (13%). Below this entry. 85.0%–90.0%: 99 US counties (10%). Below this entry. 90.0%–95.0%: 117 US counties (12%). This entry sits in this band. 95.0%–100.0%: 70 US counties (7%). Above this entry. 100.0%–105.0%: 7 US counties (1%). Above this entry. This county 0.0% 100% every floor-qualified US county, bucketed by value

Each bar is a band; taller bars hold more US counties. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count, share, and where it sits relative to this entry.

Source U.S. Environmental Protection Agency, Air Quality System (AQS) · 2025

Pollutant Breakdown

Days where each pollutant was the primary driver of AQI readings in Hill County.

Hill County, Montana criteria pollutant distribution Stratified-band visualization showing the share of monitored days each criteria pollutant (PM2.5, PM10, O3, NO2, CO) was the primary AQI driver. PM2.5 · 100.0% 0% 25% 50% 75% 100% Hill County, Montana · 304 monitored days Criteria pollutant column
  • PM2.5 · 304 days · 100.0%

2024 daily-monitor rhythm in Hill County

Month-by-month median AQI from EPA day-level county monitors (339 reported days in 2024). Jul posted the highest typical readings (median AQI 38, peak 58); Dec was cleanest at median 7. Summer months (Jun–Aug) averaged median AQI 29 vs 15 in Dec–Feb.

0 10 20 30 40 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 20 19 19 16 14 14 38 36 13 11 10 7
Hill County median daily AQI by calendar month (2024, EPA daily county file)

Health Impact Assessment

Excellent

Hill County's air quality is rated Excellent based on 92.1% good air days. There were 1 unhealthy days in 2025 when outdoor activity should be limited.

Air quality is acceptable most days, but 1 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 157. Sensitive groups should monitor real-time conditions at AirNow.gov.

The dominant pollutant is PM2.5, driving AQI on 304 of 304 monitored days.

5-Year Air Quality Trend

Air quality is improving in Hill County. Highest Good-day share: 2024 (92.6%, 314 of 339 monitored days).

Year Good Moderate USG Unhealthy Median AQI
2023 170 38 2 3 23
2024 314 23 2 0 15
2025 280 22 1 1 14

How does Hill County compare?

How Hill County compares

Good-day share better than typical
Hill County 92.1%
Beaverhead County, Montana 94.7%
Typical US county 76.0%
Median AQI better than typical
Hill County 14
Beaverhead County, Montana 13
Typical US county 39
Unhealthy days / yr about typical
Hill County 1
Beaverhead County, Montana 0
Typical US county 1

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 Hill County, Montana · 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.