What is the county seat of Washington County?

The county seat of Washington County is Hillsboro.

Is there an online parcel map for Washington County?

Yes. Washington County publishes a parcel map of 200,946 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 1843 from Tuality County, Twality County, Tualitz County and Falatine County. Since then the Atlas of Historical County Boundaries records 20 later changes, chiefly involving Columbia County, Yamhill County and Clackamas County. It was formerly called Tuality District and Tuality.

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 41067

Washington CountyOregon

Washington County is located in Oregon and was established on July 5, 1843, as Tuality District, one of four original counties created by the Provisional Legislature of Oregon Territory. The county seat is Hillsboro.

Founded1843
County seatHillsboro
Named forGeorge Washington
Land area724 sq mi + 2.4 sq mi water
Population600,372 2020 Census
Parcels mapped200,946 checked 15 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 1843 from Tuality County, Twality County, Tualitz County and Falatine County

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

Tuality District was created as one of four original Oregon counties on July 5, 1843, and included parts of present-day Oregon, Washington, and Canada. The district was renamed Tuality County on December 22, 1845, and then renamed Washington on September 3, 1849, in honor of George Washington. Washington became an official Oregon county when the state was admitted to the Union on February 14, 1859.

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

1843
Washington County created Tuality District (now Washington) created. Tuality was one of four original counties created by the Provisional Legislature of Oregon Territory. Included parts of present Oregon, Washington, and Canada. County was also identified as Twality, Tualitz, and Falatine.
from Tualityfrom Twalityfrom Tualitzfrom Falatine
5 July 1843 · Oregon Archives, p. 26
1844
Lost territory Tuality District (now Washington) lost to Yamhill District.
to Yamhill District
26 June 1844 · Ore. Terr. Laws, general and local, 1843-1849, p. 87
1845
Renamed Tuality District (now Washington) renamed Tuality County; no change in boundaries.
formerly Tuality District
22 December 1845 · Ore. Terr. Laws, general and local, 1843-1849, p. 35
1849
Renamed Tuality renamed Washington.
formerly Tuality
3 September 1849 · Ore. Terr. Laws 1850, 2nd sess., p. 54
1859
Became part of Oregon Washington became an Oregon county when the state of Oregon was admitted to the Union and Oregon Territory was eliminated. 14 February 1859 · U.S. Stat., vol. 11, ch. 33[1859], secs. 1-2/pp. 383-384 Ore. Laws 1860, 1st reg. sess., pp. 28-30

Show all 21 changes (16 more)

1843
Washington County created Tuality District (now Washington) created. Tuality was one of four original counties created by the Provisional Legislature of Oregon Territory. Included parts of present Oregon, Washington, and Canada. County was also identified as Twality, Tualitz, and Falatine.
from Tualityfrom Twalityfrom Tualitzfrom Falatine
5 July 1843 · Oregon Archives, p. 26
1844
Changed Provisional Legislature of Oregon Territory authorized the creation of Clatsop, presumably from the northern and western portions of Tuality District (now Washington). Introduction and passage of the bill creating Clatsop appears only within the session minutes for the Journal of the Provisional Legislature (1844), and no act regarding its creation appears in the general or special laws. No boundary description for the new county is given. See 19 December 1845 for the first mappable description of Clatsop from Tuality.
ClatsopTuality
22 June 1844 · Holman, p. 25; Oregon Archives, p. 43
1844
Lost territory Tuality District (now Washington) lost to Yamhill District.
to Yamhill District
26 June 1844 · Ore. Terr. Laws, general and local, 1843-1849, p. 87
1844
Lost territory Tuality District (now Washington, Oregon) lost to creation of non-county area in Oregon Country when the Tuality boundary was redefined to run along the Columbia River. Tuality eliminated from present Washington.
to Washingtonto Tuality
27 June 1844 · Ore. Terr. Laws, general and local, 1843-1849, p. 74
1845
Gained territory Tuality District (now Washington) gained from Yamhill District and lost to Clatsop when Clatsop was defined for the first time. Boundary between Tuality District and Clackamas District redefined to run "along the middle of the main channel of the Willamette River to the center of the Columbia River at the upper mouth of the Willamette".
from Yamhill Districtfrom Clatsopfrom Clackamas District
19 December 1845 · Ore. Terr. Laws, general and local, 1843-1849, pp. 36-37
1845
Renamed Tuality District (now Washington) renamed Tuality County; no change in boundaries.
formerly Tuality District
22 December 1845 · Ore. Terr. Laws, general and local, 1843-1849, p. 35
1846
Lost territory Tuality (now Washington) lost to Yamhill.
to Yamhill
11 December 1846 · Ore. Terr. Laws, general and local, 1843-1849, p. 7
1849
Renamed Tuality renamed Washington.
formerly Tuality
3 September 1849 · Ore. Terr. Laws 1850, 2nd sess., p. 54
1854
Lost territory Washington lost to creation of Columbia.
to Columbia
16 January 1854 · Ore. Terr. Special Laws 1853, 5th reg. sess., pp. 32-33
1854
Lost territory Washington lost to creation of Multnomah, and lost to Clackamas.
to Multnomah to Clackamas
22 December 1854 · Ore. Terr. Special Laws 1854, 6th reg. sess., p. 29
1855
Gained territory Washington gained from Clatsop when Clatsop was redefined.
from Clatsop
15 January 1855 · Ore. Terr. Special Laws 1854, 6th reg. sess., p. 33
1855
Exchanged territory Washington exchanged with Yamhill when Yamhill boundaries were redefined.
with Yamhill
30 January 1855 · Ore. Terr. Special Laws 1854, 6th reg. sess., p. 46
1856
Exchanged territory Washington exchanged with Yamhill when Yamhill boundaries were redefined.
with Yamhill
21 January 1856 · Ore. Terr. Laws 1855-1856, 7th reg. sess., pp. 40-41
1857
Exchanged territory Washington exchanged with Yamhill.
with Yamhill
22 January 1857 · Ore. Terr. Laws 1856-1857, 8th reg. sess., p. 15
1859
Became part of Oregon Washington became an Oregon county when the state of Oregon was admitted to the Union and Oregon Territory was eliminated. 14 February 1859 · U.S. Stat., vol. 11, ch. 33[1859], secs. 1-2/pp. 383-384 Ore. Laws 1860, 1st reg. sess., pp. 28-30
1862
Lost territory Washington lost to Clackamas.
to Clackamas
17 October 1862 · Ore. Laws 1862, 2nd reg. sess., p. 98
1885
Exchanged territory Washington exchanged with Columbia.
with Columbia
24 February 1885 · Ore. Special Laws 1885, 13th reg. sess., p. 324
1893
Exchanged territory Washington exchanged with Clackamas, Tillamook, and Yamhill.
with Clackamas with Tillamook with Yamhill
22 February 1893 · Ore. Laws 1893, gen., 17th reg. sess., pp. 161-162
1898
Gained territory Washington gained from Columbia.
from Columbia
15 October 1898 · Ore. Laws 1898, 20th spec. sess., pp. 27-28
1901
Lost territory Washington lost to Columbia.
to Columbia
25 February 1901 · Ore. Laws 1901, 21st reg. sess., pp. 126-127
1903
Gained territory Washington gained from Columbia.
from Columbia
21 February 1903 · Ore. Laws 1903, 22nd reg. sess., pp. 151-152

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 200,946 parcels from Washington County. Drawn for tax purposes: usually within a few feet of a survey, but not a survey.
checked 15 October 2026
Address points Official

One point per address, 272,096 in all from State of Oregon — Department of Administrative Services Geospatial Enterprise Office (GEOHub) with Oregon Department of Emergency Management 9-1-1 program.
edited 16 January 2026 · checked 13 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

600,372 2020 Census count

Housing units

236,678 2020 Census count

Land area

724 square miles

Water area

2.4 square miles

People per sq mi

829 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

Washington County's official site

We have found the county's site but not its offices yet; start there.

County government

County government
The official website of Washington County.
washingtoncountyor.gov

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 1843, formed from Tuality County, Twality County, Tualitz County and Falatine County, and named after George Washington.
What is the county seat of Washington County?: The county seat of Washington County is Hillsboro.
Is there an online parcel map for Washington County?: Yes. Washington County publishes a parcel map of 200,946 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 1843 from Tuality County, Twality County, Tualitz County and Falatine County. Since then the Atlas of Historical County Boundaries records 20 later changes, chiefly involving Columbia County, Yamhill County and Clackamas County. It was formerly called Tuality District and Tuality.
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