Underwent heart bypass surgery in 1989 and angioplasty to prevent a stroke in 1998.
Was a brother of the Sigma Phi Epsilon Fraternity
Was a libertarian.
Was a spokesperson for Partnership for Drug Free of America from 1993 to 1997.
Was best friends with: Kirk Douglas, Dana Andrews, Jean Stapleton, Bobby Short, Larry Hagman and Jean Simmons.
Was considered for the role of Dr. Zachary Smith on "Lost in Space" (1965).
Was fluent in Italian.
Was so displeased with CBS's axing of "Archie Bunker's Place" (1979) in 1983, without a chance to film an actual series finale, that he vowed to never work for the network again. (Nonetheless, his late-1980s NBC series, "In the Heat of the Night" (1988) later moved to CBS in 1992.)
While attending University of Montana, O'Connor was an associate editor for the college newspaper, the Kaimin. In 1949, he resigned his editing position in protest to the pressure from the campus administration that lead to confiscation and destruction of an issue of the paper, which carried a cartoon depicting the Montana Board of Education as rats gnawing at a bag of university funds.
While playing Archie Bunker he always wore his wedding ring on his middle finger and not the traditional ring finger.