The Multnomah and the related Clackamas tribe lived in a series of villages along the river near the mouth of the Willamette River on the Columbia (the Willamette was also called the "Multnomah" in the early 19th century). According to archaeologists, the villages in the area were home to approximately 3,400 people year-round, and as many as 8,000 during fishing and wappato-harvesting seasons (wappato was a marsh-grown plant like a potato or onion and a staple food).
One of the larger villages, Cathlapotle was located in present-day Clark County, Washington at the confluence of the Lewis River with the Columbia and was visited by the Lewis and Clark Expedition in 1805. According to their journals, Lewis and Clark found 14 houses in the village, most of them ranging from 14-by-20 ft (4.3 m by 6.0 m) to about 40-by-100 ft (12 m by 30 m). They reported that approximately 900 people lived in the villages.
The Multnomah diet included salmon, eels, sturgeon, elk, water birds and especially wapato. Ruby, Robert H.; John A. Brown (1992). A Guide to the Indian Tribes of the Pacific Northwest. Norman: University of Oklahoma Press.