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.
The rest of the county is described by its location relative to Seattle and Lake Washington.
North King County
Largely upscale suburbia, heavily residential.
East King County
Better known as the Eastside, this is the fastest growing region in the county.
South King County
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, (IATA: SEA), 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.
Buses in downtown Seattle are free between 6AM and 7PM in the downtown core of Seattle. Just get on and get off. To read the details refer to Metro Free Bus info .
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:
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.
Urban King County
Rural King County