SeaTac is located in southern King County, bordered by Tukwila to the east, Burien to the west, Des Moines to the south, and Seattle and Tukwila to the north. It is situated on the Highline Ridge, an elevated landmass separating Puget Sound to the west from the Green River Valley to the east.
The city encompasses approximately 9.3 square miles, a significant portion of which is occupied by the Seattle-Tacoma International Airport and its associated facilities. Despite its highly urbanized and industrial core, SeaTac contains pockets of natural beauty. The most prominent natural feature is Angle Lake, an L-shaped, 102-acre glacial lake in the southern part of the city. The city is also home to the Highline SeaTac Botanical Garden, which preserves heritage plants and water features that were relocated to save them from airport runway expansions.