On-site septic systems in King County, by city
As of September 2026, 14% of homes — about 83,959 of the 607,268 on record across the 45 King County cities VetTheHome tracks — are homes on an on-site septic system rather than municipal sewer, per public records aggregated by VetTheHome.
Updated September 2026 · refreshed weekly
Share of homes on an on-site septic system rather than municipal sewer. By city.
| # | City | Homes on record | On septic |
|---|---|---|---|
| 1 | Preston | 120 | 98% |
| 2 | Fall City | 1,906 | 98% |
| 3 | Ravensdale | 1,407 | 98% |
| 4 | Baring | 251 | 94% |
| 5 | Vashon | 5,438 | 91% |
| 6 | Woodinville | 10,931 | 76% |
| 7 | Carnation | 3,122 | 64% |
| 8 | North Bend | 6,193 | 63% |
| 9 | Skykomish | 537 | 51% |
| 10 | Enumclaw | 8,440 | 45% |
| 11 | Duvall | 5,174 | 32% |
| 12 | Maple Valley | 12,895 | 32% |
| 13 | Auburn | 28,072 | 30% |
| 14 | Issaquah | 12,354 | 29% |
| 15 | Black Diamond | 4,273 | 24% |
| 16 | Redmond | 22,904 | 23% |
| 17 | Renton | 39,273 | 20% |
| 18 | Normandy Park | 2,548 | 19% |
| 19 | Covington | 7,373 | 19% |
| 20 | Kent | 34,198 | 18% |
| 21 | Burien | 14,542 | 16% |
| 22 | Seatac | 6,570 | 16% |
| 23 | Snoqualmie | 5,450 | 16% |
| 24 | Federal Way | 23,519 | 16% |
| 25 | Sammamish | 21,611 | 15% |
| 26 | Newcastle | 4,019 | 12% |
| 27 | Des Moines | 8,768 | 11% |
| 28 | Tukwila | 5,302 | 8.8% |
| 29 | Pacific | 1,991 | 4.9% |
| 30 | Kirkland | 24,716 | 4.8% |
| 31 | Kenmore | 7,540 | 3.9% |
| 32 | Bothell | 7,213 | 3.8% |
| 33 | Bellevue | 34,471 | 3.5% |
| 34 | Lake Forest Park | 5,052 | 3.4% |
| 35 | Milton | 451 | 2.0% |
| 36 | Seattle | 198,865 | 0.5% |
| 37 | Medina | 1,256 | 0.2% |
| 38 | Shoreline | 17,460 | 0.1% |
| 39 | Algona | 1,214 | 0.0% |
| 40 | Beaux Arts | 122 | 0.0% |
| 41 | Clyde Hill | 1,136 | 0.0% |
| 42 | Hunts Point | 196 | 0.0% |
| 43 | Mercer Island | 7,857 | 0.0% |
| 44 | Snoqualmie Pass | 101 | 0.0% |
| 45 | Yarrow Point | 437 | 0.0% |
Sources: King County on-site septic (OSS) records; King County parcel records. Compiled and refreshed weekly by VetTheHome. Aggregate covers the 45 King County cities in our dataset; see the full methodology.
What this means for buyers
A septic system is the buyer’s responsibility to maintain and eventually replace — often a five-figure cost — and can constrain additions. Confirm the system type and its service history on the seller’s Form 17.
Check any King County address
More King County data
About this data
These are aggregate figures compiled from Washington public records for general information — estimates and counts, not appraisals, inspections, or legal advice. The county roll-up covers the cities in our dataset and excludes unincorporated areas; individual parcels are reported at the address level. Public records contain errors — found one? Email corrections@vetthehome.com.