When was King County founded?

King County was founded in 1852, formed from Thurston County, and named after Martin Luther King Jr..

What is the county seat of King County?

The county seat of King County is Seattle.

Is there an online parcel map for King County?

Yes. King County publishes a parcel map of 639,334 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.

Has King County's boundary or name changed?

King County was created in 1852 from Thurston County. Since then the Atlas of Historical County Boundaries records 11 later changes, chiefly involving Pierce County, Jefferson County and Kitsap County.

Is my lot in a flood zone?

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

County · code 53033

King CountyWashington

King County is located in Washington and has Seattle as its seat. It was created in 1852 from Thurston County.

Founded1852
County seatSeattle
Named forMartin Luther King Jr.
Land area2,115 sq mi + 192 sq mi water
Population2,269,675 2020 Census
Parcels mapped639,334 checked 15 October 2026

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

Updated 20 October 2026

Census outline · seat marked

History

Formed in 1852 from Thurston County

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

King County was created by Oregon Territory on December 22, 1852, from Thurston County. After the territory was reorganized, King County was attached to Pierce County for judicial purposes in 1853, and then became independent as a county in Washington Territory. Throughout its early years, King County exchanged and gained territory with neighboring counties including Pierce, Jefferson, and others. When Washington became a state in 1889, King County continued as a county of the new state.

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

1852
King County created King created by Oregon Territory from Thurston.
from Thurston
22 December 1852 · Ore. Terr. Special Laws 1852, 4th reg. sess., p. 41
1853
Became part of Washington King became a county in Washington Territory; eliminated from Oregon Territory. 2 March 1853 · Wash. Terr. Laws, 1854, 1st. sess., p. 32; Van Zandt, 155
1854
Gained territory King gained from Thurston, exchanged with Jefferson, lost to creation of Sawamish (now Mason).
from Thurston from Jefferson from Sawamishfrom Mason
13 March 1854 · Wash. Terr. Laws 1854, 1st sess., pp. 470, 474
1855
Lost territory King lost to Pierce.
to Pierce
25 January 1855 · Wash. Terr. Laws 1854, 2nd sess., pp. 39-40
1889
Became part of Washington King continued as a Washington county when the state of Washington admitted to the Union and Washington Territory eliminated. 11 November 1889 · U.S. Stat., vol. 25, ch. 180[1889], p. 676; U.S. Stat. pres. proc., vol. 26[1889], p. 10; Van Zandt, 155-156

Show all 14 changes (9 more)

1852
King County created King created by Oregon Territory from Thurston.
from Thurston
22 December 1852 · Ore. Terr. Special Laws 1852, 4th reg. sess., p. 41
1853
Changed King attached to Pierce for judicial purposes. Attachment reconfirmed 1 February 1853.
Pierce
24 January 1853 · Ore. Terr. Special Laws, 1852, 4th reg. sess., pp. 37, 52
1853
Changed King (Washington) attachment to Pierce reconfirmed.
Pierce
1 February 1853 · Ore. Terr. Laws 1852, 4th reg. sess., p. 52
1853
Became part of Washington King became a county in Washington Territory; eliminated from Oregon Territory. 2 March 1853 · Wash. Terr. Laws, 1854, 1st. sess., p. 32; Van Zandt, 155
1854
Gained territory King gained from Thurston, exchanged with Jefferson, lost to creation of Sawamish (now Mason).
from Thurston from Jefferson from Sawamishfrom Mason
13 March 1854 · Wash. Terr. Laws 1854, 1st sess., pp. 470, 474
1855
Lost territory King lost to Pierce.
to Pierce
25 January 1855 · Wash. Terr. Laws 1854, 2nd sess., pp. 39-40
1857
Lost territory King lost to creation of Slaughter (now Kitsap).
to Slaughterto Kitsap
16 January 1857 · Wash. Terr. Laws 1856, 4th sess., p. 52
1859
Exchanged territory King exchanged with Pierce.
with Pierce
29 January 1859 · Wash. Terr. Laws 1858, 6th sess., p. 59
1861
Lost territory King lost to creation of Snohomish.
to Snohomish
14 January 1861 · Wash. Terr. Laws 1860, 8th sess., p. 19
1866
Exchanged territory King exchanged with Pierce.
with Pierce
9 January 1866 · Wash. Terr. Laws 1865-1866, 13th sess., p. 143
1867
Boundary clarified King redefined (no change).
no change
31 January 1867 · Wash. Terr. Laws 1866-1867, 14th sess., pp. 46-47
1869
Boundary clarified King redefined (no change).
no change
2 December 1869 · Wash. Terr. Laws 1869, 2nd biennial sess., sec. 1/pp. 293-294
1889
Became part of Washington King continued as a Washington county when the state of Washington admitted to the Union and Washington Territory eliminated. 11 November 1889 · U.S. Stat., vol. 25, ch. 180[1889], p. 676; U.S. Stat. pres. proc., vol. 26[1889], p. 10; Van Zandt, 155-156
1901
Lost territory King lost to Pierce by virtue of an election on this date. Previous line between King and Pierce split the Tacoma harbor between the two counties; the annexation shifted the entire harbor to Pierce.
to Pierce
12 March 1901 · Gov. Proc., Wash. State Archives, Gov. Daily Record Book, Vol. 1, pp. 1-3; Rem. & Bal. Code 1909, vol. 2, ch. 1/p.243

Land and parcels

What the maps cover in King

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

Parcels Good enough

Lot lines and tax-map numbers for 639,334 parcels from King County. Drawn for tax purposes: usually within a few feet of a survey, but not a survey.
checked 15 October 2026
Address points Missing

No public address points layer found for King County yet.
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

King by the Census

Population

2,269,675 2020 Census count

Housing units

969,234 2020 Census count

Land area

2,115 square miles

Water area

192 square miles

People per sq mi

1,073 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

King 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 King County.
kingcounty.gov

See your own lot on these maps

Open King 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 King County

When was King County founded?: King County was founded in 1852, formed from Thurston County, and named after Martin Luther King Jr..
What is the county seat of King County?: The county seat of King County is Seattle.
Is there an online parcel map for King County?: Yes. King County publishes a parcel map of 639,334 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has King County's boundary or name changed?: King County was created in 1852 from Thurston County. Since then the Atlas of Historical County Boundaries records 11 later changes, chiefly involving Pierce County, Jefferson County and Kitsap County.
Is my lot in a flood zone?: We do not have flood maps for King County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

Nearby