Adopted in the 11th Report of the Geographic Board of Canada, 30 June 1912.

Source: BC place name cards, correspondence and/or research by BC Chief Geographer & Geographical Names Office staff.

U.S. Board on Geographic Names recommended that the British Columbia portion of the river be changed to "North Fork of Flathead River" as requested by some U.S. residents. Name change proposal rejected: the 12 July 1967 reply from Canada to U.S. Board stated that the channel in British Columbia will continue to be named "Flathead River" (file F.1.59) The name "Flathead River" confirmed for the British Columbia portion of the watercourse following another review in 1972. (file F.1.59).

Source: BC place name cards, correspondence and/or research by BC Chief Geographer & Geographical Names Office staff.

Named after the Flathead (Salish) Indians of Montana.

Source: 17th Report of the Geographic Board of Canada, 31 March 1921 (supplement to the Annual Report of the Dept of the Interior, 1922, Ottawa)

"Named after the Flathead tribe of Indians of Western Montana. Unlike some tribes on the Coast they do not flatten the heads of their children. The name was probably applied to them because they had some slaves from the Coast with deformed heads."

Source: Provincial Archives' Place Names File ("the Harvey File") compiled 1945-1950 by A.G. Harvey from various sources, with subsequent additions

"Named after the Flathead Indians who dwell in this district. The Flatheads have never artifically flattened the heads of their children by binding. Probably early explorers saw slaves of the Flatheads from the Pacific Coast tribes who did have deformed heads and, under a misapprehension, gave the tribe this misnomer. The Flathead River was once known as Clark's River."

Source: Akrigg, Helen B. and Akrigg, G.P.V; "1001 British Columbia Place Names"; Discovery Press, Vancouver 1969, 1970, 1973.