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Mason County, Washington

A shallow water table limits basements on 45% of Mason County's mapped land, a higher share than 62% of US counties and the 6th highest of 39 Washington counties. Shrink-swell clay limits houses without basements on under 1%.

21.6% of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 54 flood losses here since 2016, 2% of them in buildings with basements. 37% of homes were built before 1980, against 50% nationally; the median home dates from 1989.

Data as of October 13, 2026 · sources

<1%

expansive clay: shrink-swell limits slab homes

45%

high water table: limits basements

22%

in drought, October 13, 2026

37%

of homes built before 1980

Soil under Mason County

Expansive clay (limits slab homes)0.4%
High water table (limits basements)44.6%
Septic fields very limited92.9%
Clay swell (LEP, by area)1.6%
High-swell land (LEP 6%+)0.4%
Mapped soil588,968 acres
Soil seriesShare hereSeries nationally: high water table
Alderwood15%n/a
Grove11%n/a
Shelton9%n/a
Hoodsport7%n/a
Everett4%n/a
Tebo4%n/a
Kitsap County: 65%Thurston County: 34%Grays Harbor County: 20%Jefferson County: 39%Pierce County: 34%Island County: 65%Pacific County: 19%Clallam County: 42%Mason County KitsapThurstonGrays HarborJeffersonPierceIslandPacificClallamMason
Mason County (heavy outline) and nearby counties, shaded by high water table share.under 10%10-25%25-40%40-60%60%+

How we count · survey areas WA632 (2025-08-28), WA645 (2025-08-28)

What the numbers mean here

On 45% of Mason County's mapped land, soil stays saturated within about 6 feet of the surface for part of the year, which is basement depth.

Rain over the 12 months to August 2026: 83.84 in, 8.06 in below the 1991-2020 average year of 91.90 in.

USDA rates 93% of the land very limited for septic absorption fields.

Drought

21.6% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 23 of the last 52 weeks; the most was 97.5% of its area, on the October 14, 2025 map.

October 21, 2025Share of area in drought, weeklyOctober 13, 2026
Category, October 13, 2026Share of county
D0 abnormally dry or worse88.7%
D1 moderate drought or worse21.6%
D2 severe or worse0%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

54 flood losses since 2016, $2.3 million paid. The worst year was 2022, with 40. Foundations of the buildings, where recorded: 2% basements, 31% slabs, 54% crawl spaces, 13% elevated. Median water depth outside the building: 12 in.

YearFlood losses
20163
20172
20181
20190
20200
20211
202240
20234
20242
20251
2026 to date0

Rain

Average year, 1991-202091.90 in
12 months to August 202683.84 in (-8.06)
202579.43 in (-12.47)
Wettest year since 18951997: 117.28 in
Driest year since 18951930: 51.81 in
Days with 1 inch or more, normal at CUSHMAN POWERHOUSE #2 (1 mi away)29.8

Homes

Housing units34,152
Median year built1989
Built before 198037%
Built 2000 or later28%
Owner-occupied82%
Median value, owner-occupied$411,800
Single-family detached76%

What repairs cost

Published ranges from cost guides, not quotes. More sources, and where they disagree.

WorkRangeSource
Basement waterproofing, US $3,000 to $10,000 Fixr, February 6, 2026
Sump pump installation, US $800 to $2,000 Fixr, January 31, 2025
Crawl space encapsulation, US $2,000 to $8,000 Fixr, August 29, 2025

Nearby counties

PlaceDistanceExpansive clayHigh water table
Kitsap County, WA 32 mi under 1% 65%
Thurston County, WA 33 mi 3% 34%
Grays Harbor County, WA 35 mi 6% 20%
Jefferson County, WA 35 mi 1% 39%
Pierce County, WA 52 mi 2% 34%
Island County, WA 61 mi 0% 65%
Pacific County, WA 62 mi 4% 19%
Clallam County, WA 62 mi 1% 42%

Sources: USDA SSURGO (August 28, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status