During the Spanish Period, Bakun was a rancheria (towns) of the Commandancia Politico-Militar de Amburayan while Ampusongan (currently a barangay of Bakun) was a rancheria of the Commandancia Politico Militar de Tiagan, Distrito de Benguet. In 1900, when the United States took control of the Philippines, the American Congress (or Philippine Commission?) enacted Act No. 48, placing Bakun under the Province of Amburayan and Ampusongan under the province of Benguet. On August 13, 1908, the municipal districts of Bakun and Ampusongan became part of Benguet, a sub-province of Mountain Province (which was organized into several sub-provinces: Apayao, Kalinga, Bontoc, Ifugao, Benguet, Lepanto, and Amburayan), by virtue of Act No. 1876.
In 1917, the Bureau of Non-Christian Tribes recommended that the western border of the Mountain Province be pushed eastward, such that the entire subprovince of Amburayan and large slices of Lepanto and Benguet would be made part of Ilocos Sur and La Union. In the early part of 1937, Ampusongan was merged with Bakun, the latter carrying the name of the township while the former became a barangay. Bakun existed until the enactment of Republic Act No. 4695 in 1966 when it was included in the newly created province of Benguet.