Atfalati ranged around the valley, engaged in a hunter-gather lifestyle, and may have inhabited land as far east as what is now Portland. Primary food stuffs included deer, camas root, fish, berries, elk, and various nuts. To encourage the growth of the camas plant and maintain habitat beneficial to deer and elk, the group burned the valley floor to discourage the growth of forests, a common practice among the Kalapuya. Little is known of the Atfalati native customs. Their language was studied by Albert Samuel Gatschet, and most of what has been learned of the Kalapuyan tongue is from the Atfalati dialect.
Euro-Americans began arriving in the Atfalati's homeland in the early 19th century, and settlers in the 1840s. By this time diseases had decimated Native populations in the Pacific Northwest, including the Atfalati. It is estimated that the band was reduced to a population of around 600 in 1842, and had shrunk to only 60 in 1848. The United States government negotiated a treaty in 1851 with the group to allow for a small reservation on Wapato Lake, but the treaty was never ratified. In 1855, the government negotiated a new treaty with the larger Kalapuya group that included the Atfalati tribe. This treaty removed the Atfalati to the Grand Ronde Indian Reservation in the western part of the Willamette Valley at the foothills of the Oregon Coast Range where they lived with a variety of other tribes. After their removal to the reservation, tribal numbers have dwindled to about 20.