Check tomorrow's forecast
AirNow posts an air quality forecast by ZIP code, usually the day before.
AirNow →Air quality in Williamson County, TN
Includes Franklin · EPA monitor readings, 2021 to 2025 (ozone only) · 248,000 people
For today's air and tomorrow's forecast, check AirNow by ZIP code.
Bad-air days a year
<1
day with an AQI over 100
4 bad-air days in 5 years of readings, 2021 to 2025. That's down from about 25 a year in the early 2000s. Williamson County has the 8th most bad-air days of the 23 Tennessee counties with monitors.
0days unhealthy for everyoneAQI over 150, a year
41AQI on a typical dayGood: fine for everyone
6bad-air days since 2016Too few to show a season
122worst day since 2016Jun 9, 2023, ozone
How to read the AQIThe EPA's air score runs from 0 to 500. Higher is worse. Over 100 counts as a bad-air day.
Typical day 41 (Good)Worst day 122 (Unhealthy for sensitive groups)
Good0 to 50Moderate51 to 100Sensitive groups101 to 150Unhealthy151 to 200Very unhealthy201 to 300Hazardous301 to 500
Bad-air days by month in Williamson County
Bad air is rare here: 6 bad-air days in 10 years of daily readings since 2016, too few to show a season. Each tile is the average for that month.
Jan0
Feb0
Mar0.1
Apr0
May0
Jun0.5
Jul0
Aug0
Sep0
Oct0
Nov0
Dec0
The worst day since 2016 was June 9, 2023: AQI 122, from ozone.
What causes it
Ozone is the only pollutant measured here. The 6 bad-air days since 2016 were all ozone days, between June 2016 and June 2023. Monitors here don't measure fine particles, so smoky days aren't in these counts.
CDC's model estimates about 0.6 days a year with high fine particles at the county's worst spot, 2018 to 2022. See the estimates on the map
CDC estimates by month, 2001 to 2022
The CDC's model counts bad-air days at the county's worst spot, from monitors and satellites. Particles (brown) fill the inside of the ring and ozone (blue) the outside.
See the numbers by month
| Month | Fine particles | Ozone |
|---|---|---|
| January | 0 | 0 |
| February | 0 | 0 |
| March | 0 | 0 |
| April | 0 | 0.8 |
| May | 0 | 1.1 |
| June | 0.2 | 2.9 |
| July | 0.2 | 1.4 |
| August | 0.1 | 2.6 |
| September | 0.1 | 1.1 |
| October | 0 | 0 |
| November | 0 | 0 |
| December | 0 | 0 |
What helps in Williamson County
The air here is clean most days: 6 bad-air days in 10 years of daily readings. Wildfire smoke can still drift in from far away, so it's worth being ready.
Keep a cheap backup
A box fan with a MERV 13 filter clamped to it cleans a room in a pinch.
Build one →Keep one room clean on smoky days
Shut the windows and run an air purifier sized for the room.
Choosing a purifier →For today's reading and tomorrow's forecast, check AirNow by ZIP code. Its fire and smoke map adds smoke plumes.
Smoky days are rare here, so a purifier is optional. If you want one for wildfire season anyway, see the 3 models we'd buy, each with a verified smoke rating.
Every year since 2000
Bad-air days each year. The striped part is days unhealthy for everyone, over AQI 150. The worst recent year was 2022, with 2 bad-air days.
Unhealthy for sensitive groups (101 to 150)Unhealthy or worse (over 150)
See the numbers by year
| Year | Bad-air days | Over 150 |
|---|---|---|
| 2000 | 45 | 8 |
| 2001 | 19 | 0 |
| 2002 | 37 | 10 |
| 2003 | 20 | 1 |
| 2004 | 5 | 0 |
| 2005 | 19 | 0 |
| 2006 | 6 | 0 |
| 2007 | 33 | 3 |
| 2008 | 3 | 0 |
| 2009 | 1 | 0 |
| 2010 | 9 | 0 |
| 2011 | 6 | 0 |
| 2012 | 7 | 0 |
| 2013 | 0 | 0 |
| 2014 | 1 | 0 |
| 2015 | 0 | 0 |
| 2016 | 1 | 0 |
| 2017 | 0 | 0 |
| 2018 | 1 | 0 |
| 2019 | 0 | 0 |
| 2020 | 0 | 0 |
| 2021 | 0 | 0 |
| 2022 | 2 | 0 |
| 2023 | 2 | 0 |
| 2024 | 0 | 0 |
| 2025 | 0 | 0 |
Williamson County and its neighbors
Bad-air days a year, 2021 to 2025. Tennessee counties with monitors averaged about 3 bad-air days a year, weighted by population.
Nearest county with a full report: Montgomery County, TN (under 1 bad-air day a year).
Questions people ask about air in Williamson County
How often is the air bad in Williamson County?
From 2021 to 2025, monitors in Williamson County recorded about 1 bad-air day a year with an AQI above 100, which is unhealthy for sensitive groups or worse. The worst year in that stretch was 2022, with 2 bad-air days.
What causes bad air in Williamson County?
The 6 bad-air days since 2016 were all ozone days, between June 2016 and June 2023. Monitors here don't measure fine particles, so smoky days aren't in these counts.
Where can I see today's air quality in Williamson County?
AirNow, run by the EPA and its partners, shows the current AQI and tomorrow's forecast for your ZIP code. Its fire and smoke map adds smoke plumes. On a typical day the AQI in Williamson County is about 41, which is good, fine for everyone. Bad days are rare here, so check it when wildfire smoke is in the news.
About these numbers
Day counts come from the EPA's county air quality summaries, which take the worst reading across a county's monitors each day. Monitors here reported on about 242 days a year from 2021 to 2025; some run only in ozone season, so a few bad days can go uncounted. A county is large, and your street can be cleaner or worse. CDC's model, which estimates every county from monitors and satellites, gives the worst spot in Williamson County about 1 high-particle day and about 1 high-ozone day a year from 2018 to 2022.
Sources: EPA AirData county AQI summaries (2000 to 2025) and daily county AQI (2016 to 2025); CDC Environmental Public Health Tracking Network modeled PM2.5 and ozone (2001 to 2022). Updated November 8, 2026.