Read this before the number. NOAA's analysts trace smoke aloft, in satellite imagery. A plume drawn over a county does not mean smoke reached the ground there — it routinely travels thousands of kilometres at altitude with no surface impact at all. These are overhead days, not exposure. Cameron County, TX makes the point: 1,147 smoke days, 1 of them heavy.
Type at least two letters. 3,221 counties, 2,397 days analysed.
What the national picture looks like
Of 3,221 counties, 3,138 have had at least one day under smoke NOAA classed as heavy. The median county sits at 732 smoke days since 2020 — roughly 31% of all days in the archive.
The extremes tell you why the caveat above matters more than the ranking. Cameron County, TX leads on raw days at 1,147, with 1 heavy. Jackson County, OR has 101 heavy days from 440 total. The first is mostly high, thin, transported smoke. The second is what it looks like when a fire is close.
Why this exists
Smoke does not leave when the sky clears. It deposits into carpet, upholstery and bedding and re-emits for weeks, which is the part of this subject that belongs to a site about the room you spend a third of your life in. A cumulative count is a better description of that load than any single day's air-quality index.
What nobody has measured is the other half: whether any cleaning method removes wildfire smoke residue from mattress foam. Not that it does not work — nobody has asked. That gap is recorded in the intervention gap, and what is known about the chemistry sits in the smoke that stays.
Source, licence and limits
Built from the NOAA/NESDIS Hazard Mapping System smoke-plume archive, public domain, point-in-polygon against US Census county centroids. Free to reuse with attribution: the index is downloadable under CC BY 4.0.
Three limits travel with every figure. The plumes are hand-drawn by analysts, so this is expert judgement rather than instrument output. Satellite capability improved across the archive, so a rising count may be better detection rather than more smoke — compare counties within a year far more confidently than years within a county. And a county is represented by a single point, which for a large western county is a crude stand-in.
To turn an overhead day into a defensible exposure day, pair it with measured surface PM2.5 from EPA's daily county files. Overhead plus elevated surface PM2.5 is a smoke-impact day. Overhead alone is not.