[3] When Europeans arrived in the region that would become King County, it was inhabited by several Coast Salish groups.

"[17] Because only the state can charter counties, the change was not made official until April 19, 2005, when Governor Christine Gregoire signed into law Senate Bill 5332, which provided that "King county is renamed in honor of the Reverend Doctor Martin Luther King, Jr." effective July 24, 2005.

[22][23] The new logo design was developed by the Gable Design Group and the specific image was selected by a committee consisting of King County Executive Ron Sims, Council Chair Larry Gossett, Prosecutor Norm Maleng, Sheriff Sue Rahr, District Court Judge Corrina Harn, and Superior Court Judge Michael Trickey.

[28] King County has been identified as vulnerable to higher risks of flooding caused by climate change due to the number of waterways in the area.

[29] Since the mid-2000s, the county government has adopted policies to mitigate the effects of climate change and reduce carbon dioxide emissions in the region.

[30] Metro was the seventh-largest transit bus agency in the United States by ridership in 2019, with 121.3 million annual passenger trips and 400,000 per weekday.

[54] The Muckleshoot Indian Reservation is located southeast of Auburn and is home to a resident population of 3,606 as of the 2000 census.

[57] King County has the third largest population of homeless or unsheltered people in the United States according to the U.S. Department of Housing and Urban Development (HUD).

[61] Approximately 57 percent of the homeless population counted by HUD in King County was classified as unsheltered, either living in vehicles, encampments in public spaces, or other places.

[62] The number of unsheltered individuals increased significantly in the late 2010s, leading to clearing of encampments and other structures by local governments.

[63][64] The county has 5,115 emergency shelter beds and tiny house villages, of which 67 percent are in the city of Seattle.

[66] Additional shelters, parking lots, and encampment sites are operated by charity organizations and churches in the area;[67] during severe weather events such as heat waves and cold snaps, local governments open additional shelter spaces, but these often reach capacity.

[68] In 2021, a total of $123 million was spent on homelessness services by local governments in King County, including cities and the regional authority.

[65] The regional authority's five-year plan, released in 2023, estimates that $8 billion in capital costs would be required to build and staff 18,205 new units of temporary and transitional housing to address the homelessness crisis.

The county government manages elections, records, licensing, parks, wastewater treatment, and public health, among other duties.

It also handles the criminal legal and incarceration system for all cities and unincorporated areas within King County.

[75] King County is part of four congressional districts that each elect a member of the United States House of Representatives; the boundaries are redrawn every 10 years based on the results of the decennial census.

[78][79] The majority of state legislators from King County are Democrats; only four House members and two senators are from the Republican Party.

The Port of Seattle owns and operates many properties on behalf of King County's citizens, including Sea-Tac International Airport; many seaport facilities around Elliott Bay, including its original property, publicly owned Fishermen's Terminal, home to the North Pacific fishing fleet and the largest homeport for fishermen in the U.S. West Coast;[citation needed] four container ship terminals; two cruise ship terminals; the largest grain export terminal in the U.S. Pacific Northwest; three public marinas; 22 public parks; and nearly 5,000 acres of industrial lands in the Ballard-Interbay and Lower Duwamish industrial centers.

[citation needed] The King County Council was established in 1969 and consists of nine members elected by districts to four-year terms.

No Republican presidential candidate has carried the county votes since Ronald Reagan's landslide reelection victory in 1984.

Slightly more than 29% of Washington state's population reside in King County, making it a significant factor for the Democrats in a few recent close statewide elections.

In 2004, King County gave a lead to Democrat Christine Gregoire in her 2004 victory gubernatorial election, pushing her ahead of Republican Dino Rossi, who led by 261 votes after the initial count.

In the 2020 presidential election, Joe Biden defeated Donald Trump by earning 75% of King County votes.

Governor Jay Inslee also defeated Republican challenger Loren Culp with 74% of the King County vote in the concurrent gubernatorial election.