Layton James O'Neill was born on November 30, 1927, in Glendive, Montana. Layton married Melva Jean in October of 1976, and they had six children: Marilyn, Colleen, Michael, Jenny, Dennis, and Amy.

O'Neill was employed as a health physicist with Application Engineering Company (AEC) in affiliation with the Nevada Test Site. O'Neill also worked for Environmental Restoration and Waste Management (ERWM) and for the Department of Energy (DOE). O'Neill retired in 1994.

Melva Jean O'Neill (née Davis) was born on October 21, 1951, in Carlsbad, New Mexico. Melva married Layton on December 19, 1979. Melva had one child going into the marriage: Amy and Layton had five children going into the marriage: Marilyn, Colleen, Mike, Jenny, and Dennis.

O'Neill was employed as a homemaker but had previously worked as a waitress and motel desk clerk.