The land now known as King County is the ancestral homeland of several Coast Salish peoples. The area that became Seattle was traditionally home to the Duwamish people, who lived in villages throughout the region. In eastern King County, the Snoqualmie Indian Tribe lived and thrived, while the lands along the Green and White Rivers were home to the Muckleshoot people and their ancestors.

The land now known as Pierce County was originally home to the present-day Nisqually, Puyallup, Squaxin, Steilacoom, and Muckleshoot tribes. The majority of Puyallup villages were situated in proximity to the area that would eventually develop into Tacoma, while Nisqually settlements were primarily located in what is now southern Pierce County.