SeaTac is a city in southern King County, Washington, United States. The city is an inner-ring suburb of Seattle and part of the Seattle metropol…SeaTac is a city in southern King County, Washington, United States. The city is an inner-ring suburb of Seattle and part of the Seattle metropolitan area. The name "SeaTac" is derived from the Seattle–Tacoma International Airport, itself a portmanteau of Seattle and Tacoma.