ZIP 99166 falls in Ferry County, Washington, where we hold 3,311 parcels measured as septic county-wide and 612 on sewer. We do not have a per-ZIP parcel count for this county, so this is the county total, not a count specific to ZIP 99166.
ZCTA 99166 is not entirely inside one county. Land-area share is from the 2020 Census ZCTA-to-county relationship file.
| County | Land in this ZIP | Documents held | On septic (county) | On sewer (county) |
|---|---|---|---|---|
| Ferry County, Washington | 98% | 673 | 3,311 | 612 |
| Okanogan County, Washington | 2% | 5 | 14,350 | 6,203 |
Land-area overlap is from the 2020 Census Bureau ZCTA5-to-county relationship file, not an estimate of ours. Parcel and document counts are rows we hold, not a survey of every property in the ZIP. Last verified 2026-09-01.
We hold 3,311 parcels measured as septic for Ferry County, Washington as a whole, not broken out by ZIP.
ZIP 99166 spans 2 counties: Ferry County, Washington, Okanogan County, Washington.