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.