If you are waiting for the calendar to tell you when to buy in Sonoma County, the county-wide numbers say September. Four years of MLS data show active listings holding near their yearly high through September before falling hard into winter. Break that pattern down by town, though, and September stops being the answer everywhere. Some of Sonoma County's most popular markets are already shrinking by then.
National research from Realtor.com points to the week of September 27 through October 3, 2026 as the single best week to buy nationally, with roughly 32 percent more listings on the market than at the start of the year and list prices running about 3.5 percent below their summer peak. That is a pattern built from thousands of markets averaged together. Sonoma County's own data tells a more layered story, and the county number hides real disagreement between towns.
The county-wide plateau
Look at Sonoma County as a whole and the seasonal pattern holds up well. Active listings climbed from August into September in three of the last four years, and in 2025 the county added just 14 listings between the two months, from 1,254 to 1,268. Only after September does the shelf really start to clear. From 2022 through 2025, county-wide inventory fell by an average of roughly 40 percent between September and December, and by 48.7 percent this year alone.
But the timing shifts once you leave the county view
Pull that same August-to-September comparison apart by town, and the county average turns out to be hiding real disagreement. Sebastopol grew 14.7 percent and the city of Sonoma grew 13.0 percent, both well ahead of the county's 1.1 percent. Petaluma grew a more modest 6.2 percent. Santa Rosa and Healdsburg were both essentially flat, down 2.0 percent and 3.7 percent. Windsor and the Russian River communities moved further in the same direction, falling 15.7 percent and 24.0 percent, which means their inventory had already turned over by the time the county-wide number was still climbing.
For a buyer working Windsor or the Russian River, waiting for "the usual September peak" means showing up after the best of the season's selection is already gone. For a buyer looking in Sebastopol, the city of Sonoma, or Petaluma, September and into October is still building toward more choice, not less. Healdsburg and Santa Rosa sit in between, close to flat on either side of the turn.
Winter empties the shelf everywhere, just not by the same amount
Wherever a market peaks, it eventually gives that inventory back. Every one of the eight markets we track lost at least 38 percent of its September active listings by December 2025. Sebastopol led the drop at 65.4 percent, followed by the Russian River at 57.0 percent and Windsor at 53.5 percent. Sonoma fell 50.5 percent, Santa Rosa 50.3 percent, the county overall 48.7 percent, and Petaluma 44.2 percent. Healdsburg held up best of the group, down 38.1 percent, the mildest winter drawdown of any market in the data set.
Why the shelf clears out
The mechanics are fairly simple. New listings coming onto the market stay roughly flat heading into fall, while the pace of closings slows, typically dropping by high single digits to low double digits from August into September. Fewer sales should leave more homes standing on the market, not fewer, but new supply cannot keep pace with the seasonal drop-off in fresh listings once the holidays approach, and what remains on the market by December has usually been sitting for a while. Average days on market in Sonoma County has climbed every year from August to December, from 59 days to 83 days this year, an increase of more than 40 percent. Price behaves the same way. Homes that sold in August 2025 closed at 94 percent of their original list price on average; by December that had slipped to 91 percent.
What this means if you are buying?
If you are house hunting in Windsor or along the Russian River, do not bank on a September peak that, in this market, has usually already passed. Late summer is your widest selection. If you are looking in Sebastopol, the city of Sonoma, or Petaluma, the county's broader pattern applies more directly, and you can reasonably expect more choice into September and early October. Healdsburg is the outlier worth knowing about: it barely moves in September and gives up the least ground of any Sonoma County market by December, so the calendar matters less there than it does elsewhere. Wherever you are looking, December buyers face the thinnest inventory of the year, but also the most patient sellers: longer days on market and lower prices relative to the original list, four years running.
Every one of these markets moves on its own clock, and the right week to start looking depends on which town you are watching. If you want the current read on your specific market before you start touring, email me directly at david@bruingtonhargreaves.com.
About the Author
David Hargreaves is the co-founder of BruingtonHargreaves, one of Sonoma County's top-ranked real estate teams and part of W Real Estate. Originally from the UK and an Oxford University graduate, David built and ran a digital marketing agency serving Google, Facebook, and other major brands before becoming one of Sonoma County's top agents within three years of entering real estate.
Today he and business partner Jonathan Bruington have sold more than $250 million in Sonoma County homes over the past three years, earning recognition as a RealTrends No. 2 team in the county and the No. 1 team in Healdsburg. David specialises in helping Bay Area buyers and sellers with luxury properties and vacation rentals across Healdsburg, Windsor, Santa Rosa, and the Russian River communities.
He lives in Sonoma County with his wife Nancy and is happiest cycling the back roads, exploring local wineries, or behind a camera. Have a question about buying, selling, or building in Wine Country? Book a free call.