His 19th century Dutch American ancestors; Thomas Arnold Demill (1799–1877), Henrietta Elizabeth Demill (1821–1881), William Edward Demill (1824–1873), and Richard Mead Demill (1828–1905) owned and operated a Commission Merchant (shipping and trading) company, Demill & Co. in New York City at 178-1/2 Water Street, serving the ports of the Eastern Seaboard, including but not limited to Halifax, Nova Scotia and (Little) Washington, North Carolina throughout the American Civil War. A very close family friend, J.J. Reford, was identified as a person of interest and known associate of John Wilkes Booth, the assassin of President Abraham Lincoln, as the result of a letter dated N.Y. 20th Feby/65 from Reford being discovered amongst Booth's belongings during the government's search of the actor's room at the National Hotel in Washington, D.C. as part of the official investigation after the assassination.
He served with the United States Army Air Corps from 1943 to 1946. That year, he became a writer and director at KTLA, remaining in that position through 1950. Around this time he became an early convert to the movement that was to become Scientology leaving KTLA to become an editorial/personal assistant to founder L. Ron Hubbard. De Mille used the nom de plume "D. Folgere" (an Anglo-Saxon phrase meaning "follower") when editing and/or ghost-writing during that time, despite Hubbard's protests that it would appear "Dick de Mille wasn't a true believer". Still, he remained with Hubbard through 1953, when the two men finally parted company due to "mutual dislike". He then became a freelance writer and editor. In 1955, he completed his B.A. degree at Pepperdine University and married Margaret Belgrano. He went on to get a Ph.D. from the University of Southern California in 1961. He would remain with that institution as a research psychologist until 1962, when he became a lecturer in psychology at the University of California, Santa Barbara. In 1965, he left that position, becoming editorial director of the Brooks Foundation the following year. He stayed there until 1967, becoming a research psychologist at the General Research Corp. in 1968, where he remained through 1973.
De Mille wrote Castaneda's Journey: The Power and the Allegory (publ. 1976), a book describing the detective work through which he alleged that controversial author Carlos Castaneda was a charlatan and plagiarist. He edited a second book on the same subject, The Don Juan Papers (publ. 1980), when he found that his exposé did not lead Casteneda's most ardent followers to fall away. Nor did he expect them to. This book contains documents representing views of Castaneda across the spectrum. He also wrote a biography of his birth mother, screenwriter Lorna Moon entitled My Secret Mother: Lorna Moon. Fellow writer Carol Easton (author of No Intermission: The Life of Agnes de Mille), had this to say about him and his life: "None of Richard de Mille's extraordinary relatives, not even the legendary Cecil B. de Mille himself, could have invented this riveting true story of celebrity, passion, betrayal, and tragedy".
Come Retribution. The Confederate Secret Service and the Assassination of Lincoln. William A. Tidwell with James O. Hall and David W. Gaddy. (c) 1988 University Press of Mississippi. Re: J.J. Reford and Demill & Co. 178-1/2 Water Street NYC
Investigation and Trial Papers relating to the Assassination of President Lincoln. Microcopy No. 599, Roll/Reel 2 Frames 0353-57 and Roll/Reel 3 Frame 0114. Re: J.J. Reford and Demill & Co. 178-1/2 Water Street NYC. National Archives.
The Lincoln Assassination. The Evidence. Edited by William C. Edwards and Edward Steers Jr.. (c) 2009 by the Board of Trustees of the University of Illinois. Re: J.J. Reford and Demill & Co. 178-1/2 Water Street NYC
A Lawyer On Religion. Newspaper article referencing Richard Mead Demill. Published December 19, 1908 (c) The New York Times.
The Foundation and the Superstructure: or the Faith of Christ and the Works of Man. Richard Mead Demill. (c) 1908 G.P. Putnam's Sons. 392 pages.
United States Patent No. 48,478. Horace Boardman, assignor to himself and Kelby, DeMill & Co., New York "Manufacture of Wrought iron from the Ore" dated June 27, 1865. (Annual Report of the Commissioner of Patents for the year 1865 Volume I. Washington: Government Printing Office 1867)
The War of Rebellion: A Compilation of the Official Records of the Union and Confederate Armies: Series II, Vol.III, Serial Set Vol. No. 3789, Session Vol. No. 47, Report: H.Doc.67 - Confederate Correspondence, Etc. page 702 from Jas. E. Hoyt to H.T. Pairo August 9, 1861. Re: Thomas Arnold Demill & Alfred M. Wood.
The War of Rebellion: A Compilation of the Official Records of the Union and Confederate Armies: Series II, Vol.III, Serial Set Vol. No. 3789, Session Vol. No. 47, Report: H.Doc.67 - Confederate Correspondence, Etc. pages 708 and 709 from W.E. Demill to Hon. L.P. Walker August 21, 1861. Re: Thomas Arnold Demill, Richard Mead Demill & Alfred M. Wood.
Arrival Of Captured Rebel Officers At Washington - Their Statements Regarding The Battle. Newspaper article referencing the capture of Confederate Major W.E. Demill. Published March 28, 1865. (c) The New York Times.
Henry C. de Mille, Dramatist. Obituary. Published February 11, 1893. (c) The New York Times.
Romance Of War In Play At Belasco's and De Mille War Play Returns. Newspaper articles. Published December 3, 1907 and December 29, 1908. (c) The New York Times.
Duty Of The Dramatist - William C. De Mille on Morality, Old and New, and its Treatment on the Stage. Newspaper article. Published October 1, 1911. (c) The New York Times.
De Mille Tells How To Hold The Audience. Article by Grace Kingsley. Published April 9, 1915. (c) Los Angeles Daily Times.
L.A. Confidential: The Author Was Raised By Cecil B. And Constance De Mille. Then He Found Out Who His Real Parents Were. Article by David Freeman. Published April 19, 1998.(c) New York Times.
The Secret of the Other de Mille. Article by Scott Eyman. Published April 29, 1998. (c) Cox News Service.
An Original: Richard de Mille. Article by Dr. Wallace Simpson. Published June 25, 2009. (c) Science-Based Medicine.