Wikipedia
NASFiC (1975)
NASFiC, held in Los Angeles, California, on Labor Day weekend 1975, at the Los Angeles Airport Marriott, was the first North American Science Fiction Convention. "NASFiC" was an initialism for North American Science Fiction Convention. This "Continental Convention", the first of its kind, was held because Melbourne, Australia, was selected as the location for the 1975 Worldcon.