King County is the largest county in Washington State by population, home to roughly 30% of the state's residents. It stretches from Puget Sound to the Cascade Range, encompassing the major cities of Seattle and Bellevue and their sprawling suburbs, as well as wide stretches of rural farmland and uninhabited mountain terrain.
- Seattle - The seat of King County and the Pacific Northwest's largest city, with an extensive range of attractions.
The rest of the county is described by its location relative to Seattle and Lake Washington.
North King County
Largely upscale suburbia, heavily residential.
- Bothell - Commercial center of the north county
- Lake Forest Park
- Woodinville - The center of the Washington wine industry
East King County
Better known as the Eastside, this is the fastest growing region in the county.
- Bellevue - The second largest city in King County and Seattle's largest suburb, home to an art museum and a botanical garden
- Kirkland - Charming lakefront city
- Mercer Island
- Redmond - Home to Microsoft and Nintendo of America
South King County
- Des Moines
- Federal Way
- Maple Valley
- Normandy Park
- Renton - dominated by Boeing's 737 factory
- SeaTac - the city that named itself after an airport
- White Center - blends seamlessly into its neighbor, West Seattle
The rural, sparsely distributed towns of the far east county are the one respite from the sprawl.
The major interstates are I-5, running north-south through Seattle to Snohomish County and Pierce County, and I-90, running east from Seattle through Bellevue and Issaquah to Snoqualmie Pass and Kittitas County. The notoriously congested I-405 splits off from I-5 at Tukwila in the south and Lynnwood in the north, serving Bellevue and the other cities of the Eastside. SR-167 is an alternate route from Tacoma to the south county, while SR-18 is a high speed bypass from north of Tacoma to I-90 east of Issaquah.
Seattle-Tacoma International Airport, (SEA IATA), called "SeaTac" by locals, connects Seattle to all regions of the world, with especially frequent transpacific routes. Competition is fierce and fares are low on service to the San Francisco Bay Area and Southern California.
- Washington State Ferries connect downtown Seattle to Bainbridge Island, to Bremerton, and to Vashon Island, and connects West Seattle to Vashon Island and to Southworth (Kitsap Peninsula). All ferries are for both vehicles and passenger except the ferry between downtown Seattle and Vashon Island.
- High Speed Catamaran Passenger ferries  connect Seattle to Victoria, British Columbia (Canada)
Sound Transit (diesel and hybrid buses, trains) is more expensive, but has many convenient express routes that travel South (to Tacoma), East (Redmond, Bellevue), and North (Bothell, Lynnwood). Unlike Metro, it serves the adjoining counties as well.
Outside of the immediate Seattle-Bellevue area, many routes operate only during weekday rush hours. Check your schedules in advance, and beware of holiday service cutbacks. The number of the route also tells you which area of the county it serves:
- Below 100 - Seattle only
- 100s - South King County
- 200s - Eastside
- 300s - North King County
- 500s - All Sound Transit routes
Sound Transit Link Light Rail service connects Sea-Tac Airport, Tukwila and Seattle.
Sounder commuter rail service, operating weekday rush hours only, connects Seattle to Tacoma via Kent and Tukwila.
All but essential for reaching the outermost suburbs and mountains. In addition to the interstates, major routes include SR-520, linking Seattle's University District to Bellevue and Redmond; SR-18, a major freeway in the south county from Federal Way to Issaquah; and SR-509, the alternate route from the airport to Burien and Seattle.
Traffic congestion is a major problem in the Puget Sound area on all freeways and major roads. Avoid traveling during rush hour if you can, particularly along I-5 and across the Lake Washington bridges.
Lake Washington is crossed by two floating bridges: the I-90 bridge is free, but the SR-520 bridge charges a toll that varies by the time of day. There are no toll booths: unless you have a transponder, your license plate will be recorded and a bill will be mailed to you automatically in a few weeks. The long detour around the lake in either direction will usually waste far more time than you'll save in toll money.
- the North Cascades region — north and east
- Tacoma and Pierce County — south
- the Kitsap Peninsula — west