Bacnotan is one of the original twelve towns of La Union, officially joining the province upon its creation in 1850. First founded in 1599 as part of Ilocos Sur, Bacnotan later became part of Pangasinan in 1785 before transitioning to La Union.

Local lore suggests its name came from "bakunuttan," meaning "to flog," a term associated with the overthrow of a harsh tribal chieftain. Bacnotan played key roles in resistance efforts during both the Spanish-American War and World War II, notably at Baroro Bridge.

Post-war, the town briefly served as the provincial capital and became the site of major developments like the cement industry in Quirino and the founding of Don Mariano Marcos Memorial State University in Sapilang, making Bacnotan a hub of education and industry in northern La Union.

Bacnotan is located 284 kilometers away from Manila. It is a major transit area for the Manila-Ilocos bus route 24/7. There are also jeeps and tricycles for short trips within the municipality.

Home to the National Apiculture Research, Training and Development Institute (NARTDI), it has made Bacnotan a pilot area for support, instruction, research and production on beekeeping. Based at the Don Mariano Marcos Memorial State University (DMMMSU) Main Campus, it came into existence by virtue of RA 9151 which then La Union 1st District Congressman and former Governor Manuel C. Ortega authored. Also located at DMMMSU is the Sericulture Research Development Institute which produces quality silk.