When was Washington County founded?

Washington County was founded in 1879, formed from Ada County and Boise County, and named after George Washington.

What is the county seat of Washington County?

The county seat of Washington County is Weiser.

Is there an online parcel map for Washington County?

Yes. Idaho Department of Water Resources publishes a parcel map of 11,033 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.

Has Washington County's boundary or name changed?

Washington County was created in 1879 from Ada County and Boise County. Since then the Atlas of Historical County Boundaries records 5 later changes, chiefly involving Idaho County, Adams County and Boise County.

Who issues building permits in Washington County?

The county's page on building permits: Drivers License & Concealed Weapons Permits. Inside a city or town, ask that city first.

Is my lot in a flood zone?

We do not have flood maps for Washington County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

County · code 16087

Washington CountyIdaho

Washington County is in Idaho, with its county seat in Weiser. It was created on February 20, 1879.

Founded1879
County seatWeiser
Named forGeorge Washington
Land area1,453 sq mi + 21 sq mi water
Population10,500 2020 Census
Parcels mapped11,033 checked 16 October 2026

Open the free map Click any parcel in Washington County: acreage, parcel id, address and who publishes the map. No sign-in.

Updated 20 October 2026

Census outline · seat marked

History

Formed in 1879 from Ada County and Boise County

An old deed may name a county that no longer exists, or a boundary that has since moved.

Washington County was created by Idaho Territory from Ada and Boise counties. It was named after George Washington. The county gained territory from Boise in 1883 and from Idaho in 1895, and lost territory to Adams County in 1911. When Idaho was admitted to the Union on July 3, 1890, Washington County continued as a county of the state.

Boundary changes from the Newberry Library, Atlas of Historical County Boundaries; the 5 that matter most are shown first.

1879
Washington County created Washington created by Idaho Territory from Ada and Boise.
from Ada from Boise
20 February 1879 · Id. Terr. Laws 1879, 10th sess., pp. 40-42
1883
Gained territory Washington gained from Boise.
from Boise
31 January 1883 · Id. Terr. Laws 1882, 12th sess., pp. 67-68
1890
Became part of Idaho Washington continued as an Idaho county when the state of Idaho admitted to the Union and Idaho Territory eliminated. 3 July 1890 · U.S. Stat., vol. 26, ch. 656 [1890]/pp. 215-219; Van Zandt, 156
1891
Exchanged territory Washington exchanged with Idaho.
with Idaho
11 February 1891 · Id. Laws 1890, 1st sess., pp. 41-42
1895
Gained territory Washington gained from Idaho.
from Idaho
23 February 1895 · Id. Laws 1895, 3rd sess., pp. 21-22

Show all 9 changes (4 more, mostly small adjustments)

1879
Washington County created Washington created by Idaho Territory from Ada and Boise.
from Ada from Boise
20 February 1879 · Id. Terr. Laws 1879, 10th sess., pp. 40-42
1883
Gained territory Washington gained from Boise.
from Boise
31 January 1883 · Id. Terr. Laws 1882, 12th sess., pp. 67-68
1887
Boundary clarified Washington boundaries redefined (no change).
no change
1 June 1887 · Id. Terr. Laws 1887, comp., spec. and loc., 14th sess., p. 205
1890
Became part of Idaho Washington continued as an Idaho county when the state of Idaho admitted to the Union and Idaho Territory eliminated. 3 July 1890 · U.S. Stat., vol. 26, ch. 656 [1890]/pp. 215-219; Van Zandt, 156
1891
Exchanged territory Washington exchanged with Idaho.
with Idaho
11 February 1891 · Id. Laws 1890, 1st sess., pp. 41-42
1895
Gained territory Washington gained from Idaho.
from Idaho
23 February 1895 · Id. Laws 1895, 3rd sess., pp. 21-22
1899
Boundary clarified Washington redefined (no change).
no change
2 February 1899 · Id. Laws 1899, 5th sess., pp. 22-23
1905
Boundary clarified Washington boundaries redefined (no change).
no change
27 February 1905 · Id. Laws 1905, 8th sess., pp. 303-304
1911
Lost territory Washington lost to creation of Adams.
to Adams
15 March 1911 · Id. Laws 1911, 11th sess., ch. 31/pp. 67-72

Land and parcels

What the maps cover in Washington

Who publishes each layer, how good it is, and when we last checked.

Parcels Good enough

Lot lines and tax-map numbers for 11,033 parcels from Idaho Department of Water Resources. Drawn for tax purposes: usually within a few feet of a survey, but not a survey.
checked 16 October 2026
Address points Official

One point per address, 5,235 in all from State of Idaho ArcGIS Online organization (owner pbond__idaho; Idaho Geospatial Council / Idaho Office of Information Technology Services, 'The Idaho Map').
edited 2 October 2026 · checked 14 October 2026
Buildings Reference

Roof outlines traced from aerial imagery from FEMA Response Geospatial Office with Oak Ridge National Laboratory (ORNL). Good for seeing what is on a lot; not accurate enough to set a fence from.
checked 18 October 2026

Official: from the office that keeps the record
Good enough: a reliable statewide or national copy
Fallback: a guide only; check the official record
Missing: nothing public found yet

People and land

Washington by the Census

Population

10,500 2020 Census count

Housing units

4,514 2020 Census count

Land area

1,453 square miles

Water area

21 square miles

People per sq mi

7 population ÷ land area

Source: US Census Bureau, 2020 Census; US Census Bureau, 2020 Gazetteer Files. Not endorsed or certified by the Census Bureau.

Rules and offices

Who to ask before you build, dig or sell

Official county pages only. We link to them; we do not copy them, because they change.

Inside a city or town, permits usually come from that city rather than the county.

Records

Assessor and property records 208-414-2530from co.washington.id.us · checked 13 October 2026
Clerk of court: deeds and platsfrom co.washington.id.us · checked 13 October 2026

Permits

Drivers License & Concealed Weapons Permitsfrom co.washington.id.us
Permits & Applicationsfrom co.washington.id.us

Zoning and code

Planning and zoningfrom co.washington.id.us · checked 13 October 2026
Washington County Ordinancesfrom co.washington.id.us
Calendar • Washington County Planning & Zoning Meetingfrom co.washington.id.us
Planning & Zoningfrom co.washington.id.us

County government

County government
The official website of Washington County.
co.washington.id.us

See your own lot on these maps

Open Washington County on Parcel Chart's free map and click your parcel. Save it with a free account; the full record of your place (site map, projects, documents) is Pro, in early access.

Open the free map no sign-in Pro early access

Questions

Common questions about Washington County

When was Washington County founded?: Washington County was founded in 1879, formed from Ada County and Boise County, and named after George Washington.
What is the county seat of Washington County?: The county seat of Washington County is Weiser.
Is there an online parcel map for Washington County?: Yes. Idaho Department of Water Resources publishes a parcel map of 11,033 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has Washington County's boundary or name changed?: Washington County was created in 1879 from Ada County and Boise County. Since then the Atlas of Historical County Boundaries records 5 later changes, chiefly involving Idaho County, Adams County and Boise County.
Who issues building permits in Washington County?: The county's page on building permits: Drivers License & Concealed Weapons Permits. Inside a city or town, ask that city first.
Is my lot in a flood zone?: We do not have flood maps for Washington County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

Nearby