| Surname | Given names | Year | Article Most Recent Common Ancestor (MRCA) if confirmed |
| Oakley Burris | Helen M. | 2011 | “Helen M. Burris,” obituary, Thorn-Black Funeral Home (Cambridge, Ohio), 5 Jan 2011. Spouse: Carey Burris. KFH MRCA: Jesse Thomas and Catherine “Katy” Ader |
| O’Brien Ader | Elizabeth | 1877 | “Kate Ernin Fined for Using Abusive Language Toward Lizzie Ader,” news article, The Wheeling Daily Register (Wheeling, West Virginia), 18 June 1877, p. 4, col. 3. Spouse of Allen Benjamin Ader, KFH MRCA: Ader |
| O’Brien Ader | Elizabeth | 1899 | “Pioneer Days, Mrs. Benjamin Ader Death, age 39, 24 May 1899,” news article, Steubenville Weekly Herald (Steubenville, Ohio), 19 Sept 1936, p. 6, col. 6. Spouse of Allen Benjamin Ader, KFH MRCA: Ader |
| Odenthal Brown | Jean Ann | 2009 | “Jean Ann Brown,” obituary, Press-Enterprise (Riverside, California), 16 Apr 2009. Spouse of Ralph Thomas Brown. KFH MRCA: Jesse Thomas and Catherine “Katy” Ader |
| Ogden | Earl Francis | 1988 | “Wichita Man Dies After One-Car Accident,” obituary, The Salina (Kansas) Journal, 4 July 1988, p. 9, col. 5. KFH MRCA: John T. Swafford and Elizabeth Seagraves |
| Ogden Ricke | Helen L. | 1998 | “Helen L. Ricke,” obituary, The Catholic Advance (Wichita, Kansas), 13 Mar 1998, p. 9, col. 4. KFH MRCA: John T. Swafford and Elizabeth Seagraves |
| Oliver | Richard Wilmer | 1971 | “Richard Oliver,” obituary, The Tribune (Coshocton, Ohio), 15 Dec 1971, p. 11, col. 6. Spouse of Patricia Ann Thomas, KFH MRCA: Lewis Thomas and Jenette “Jane” Savage |
| Oliver | Thomas R. | 1979 | Thomas R. Oliver, obituary, The Times Recorder (Zanesville, Muskingum County, Ohio), Feb 1979, p. 2, col. 1. KFH MRCA: Lewis Thomas and Jenette “Jane” Savage |
| Oliver Parsley | Verna Lee | 1976 | “Verna Lee Parsley,” obituary, The Times (Munster, Indiana), 6 Feb 1976, p. 16, col. 6. Spouse of Raleigh Andrew Parsley and William J “Lonnie” Parsley, both KFH MRCA: William A. Faulkner and Dianah Burton |
| O’Reilly Thomas | Winnifred Henrietta | 1993 | “Winnifred H. Thomas, obituary, The Independent-Record (Helena, Lewis and Clark County, Montana), 11 Jun 1993, p. 6, col. 2. Spouse of Douglass H. Thomas, KFH MRCA: Jesse Thomas and Catherine “Katy” Ader |
| Overton Hale | Eula Christine | 2017 | “Eula Christine Overton Hale,” obituary, Maple Hill Funeral Home website (Kansas City, Kansas), 30 Oct 2017. Spouse of Herbert Allen Hale, KFH MRCA: Thomas Younger Swafford and Elizabeth Nichols |
| Owens Ashoff | Opal Jewell | 1999 | “Opal Jewel Ashoff,” obituary, Southern Illinoisan (Carbondale, Illinois), 27 Mar 1999, p. 14, col. 2. KFH MRCA: John T. Swafford and Elizabeth Seagraves |
