King County GIS data is at:
https://gis-kingcounty.opendata.arcgis.com/ (new KCGIS Open Data site)
OR
http://www5.kingcounty.gov/gisdataportal/ (legacy KCGIS data FTP download portal)

Link to King County GIS Center Open Data site. Provides access to browse and download from hundreds of enterprise data sets. Includes links to other data sources including legacy FTP Download Portal

Maps and map applications of all kinds—interactive map viewers, downloadable maps, map collections and more—from all around King County government.

Here you will find a selection of maps that have been produced by various King County departments and divisions and are hosted on the KCGIS Center website.