Southwesterncon was a series of regional multi-genre fan conventions held annually in Texas and Oklahoma between 1966 and 1971 (and then sporadically afterward until 1981). On a rotating basis, conventions were held in Dallas ("D-Con"), Houston ("Houstoncon"), and Oklahoma City ("Multicon"). Most Southwesterncons took place over three days in June. Southwesterncon is credited with being one of the earliest ongoing comic book conventions in the United States.

The initial plan for Southwesterncon was explained by Oklahoma Alliance of Fans co-founder Bart Bush: "Dallas held the first Southwesterncon in 1966, Houston held the second one in 1967, and then it went back to Dallas in 1968. The idea is that they would each do the con every other year." Oklahoma City joined Southwesterncon in 1970.

The convention featured a large range of pop culture elements, primarily comic books but also radio and television serials, science fiction/fantasy (particularly Star Trek), film/television, animation, toys, and horror, as well as a costume contest. Nostalgia for times past played an important role: all Southwesterncon events featured screenings of classic science fiction films and old television serials. The convention featured panels with comic book professionals, and floorspace for exhibitors, including comic book dealers and collectibles merchants. The show included an autograph area, as well as an Artists' Alley where comics artists signed autographs and sold or did free sketches. (Despite the name, Artists' Alley could include writers, celebrities, and even glamour models.)

There was an earlier "Southwesterncon": a science fiction convention held in Dallas on July 5–6, 1958. Organized by Tom Reamy and James and Gregory Benford of the Dallas Futurian Society (DFS) (so named after the earlier New York Futurians), Southwesterncon was the first science fiction convention held in Texas. The professional guest of honor was Marion Zimmer Bradley. Longtime science fiction fan personality, collector, and literary agent Forrest J Ackerman came from Los Angeles and served as the convention's banquet toastmaster.

The 1958 Southwesterncon was actually the sixth edition of a regional, rotating city and state series of cons which had started as "Oklacon", editions of which had previously been held in Oklahoma City, Tulsa, and Enid. On the last day of the convention, as part of Southwestercon VI's business meeting, the members of the DFS disbanded their club (due to much behind-the-scenes intrigue and politics). That event spelled the end of the Oklacon/Southwesterncon series of science fiction conventions.

In 1966, Dallas-based comics enthusiast Larry Herndon (co-publisher of the fanzine Star Studded Comics) revived the Southerwesterncon name as a multi-genre convention with a strong comic book focus. On July 23–24, 1966, the new Southerwesterncon (originally titled "Southwestern Con") was inaugurated at Dallas' Hotel Southland. The official guest was Academy of Comic-Book Fans and Collectors executive secretary and Academy Con promoter Dave Kaler. There were approximately 70 attendees at the convention, including Tom Reamy (of the previous iteration of Southwesterncon) and Camille Cazedessus Jr. Events included a costume contest, with Howard Waldrop among the participants. The 1936 British film Things to Come was shown instead of the promised 1933 film King Kong.

Meanwhile, in 1965, Houston-based enthusiasts Ray Bonario, Marc Schooley, and Jerry Poscovsky formed the Houston Comic Collector's Association (HCCA). In 1967, the HCCA produced the second Southwesterncon, officially known as the "Houston Comic Convention", expanding it to three days and staging it at the Houston Ramada Inn on June 16–18 of that year.

Movies shown at the convention included Metropolis (1927), Shadows Over Chinatown (a 1946 Charlie Chan feature), Behind the Mask (a 1946 The Shadow feature), and Dick Tracy vs. Crime, Inc. (1941).