Historical records documenting King County's involvement in air, rail and water transportation during the twentieth century are listed below. Unless otherwise indicated, these records are held at the King County Archives. Please contact the Archives with questions about these materials, which can be found in many different records series.
King County International Airport (Boeing Field)
County Commissioner records relating to airport establishment and operations.
Maps and plans of Boeing Field and its structures. Additional graphical material at the Puget Sound [state] Regional Archives (external link).
Records and photographs relating to property acquisition for airport expansion
Records of grade crossings on county roads
Photographs of grade crossings, undercrossings and overcrossings
Great Northern Railway maps of Seattle's Salmon Bay area
Rail-to-trail records and photographs
Maps showing mainline and logging railway routes
Maps and drawings showing electricity transmission lines running adjacent to rail lines (interurban streetcars and the Milwaukee Road railroad)
ferry system ( active approximately 1900 - 1940)
County Commissioner proceedings describing actions involving county ferries
County ferry docks: plans and photographs
Administrative records, Vashon Island ferry service (1921-1925)
Financial records and audits
Vessel plans and elevations
Other Sources of Historical Public Transit Records
Between 1972 and 1996 the King County bus and trolley system was operated by the Municipality of Metropolitan Seattle ("Metro"). Transit records from this time period are held by the Puget Sound [state] Regional Archives (external link). Also at the Regional Archives are records from Metro Transit's predecessors:
Seattle Electric Company (1901-1903)
Puget Sound Traction, Light and Power Company (1912-1919)
Seattle Municipal Street Railway (1910-1937)
Seattle Transit System (1939-1971)
An online history of Metro Transit is available. Hard copies are available for viewing at the King County Archives.
The Puget Sound [state] Regional Archives (external link) also holds records of the Seattle Monorail Project (1998-2005) and the Seattle Popular Monorail Authority (2002-2005).