| O'Dochartaigh Forever: Community research centre with online newspapers and private chatroom. Includes associated links and gift emporium. |
| Oakes: Descendents of David Oaks, an early pioneer in Western North Carolina and Tennessee, USA. |
| Oddy: Sandy's Family History: Features ahnentafel chart and the surnames Oddy, Howes, Fincher and Plumley. |
| Odell: Starting point for research into the Odell name and its variants, with particular emphasis on UK roots. |
| Odendahl: Ancestral history of Theresa Marie Idica and Teresa (Terry) Anne Holmes. Features the ancestors and descendants of William R Odendahl (1822-1894) and Peter Odendahl (1817-1899). |
| Ogasawara Clan: Descendants of Ogasawara Jiro Nagakiyo (1163-1242) including associated lineages. |
| Ogbourne Chronicles: Historical information relating to the names and its variants in the UK and USA. Includes descendants of slaves owned by Charles Harrison Ogburn of Mecklenburg, Virginia. |
| Ogle: Researching the Hoffman, Ogle, Creech and Butz families; settled in the state of Kansas for the most part. |
| Okouneff: Ancestors of Sharon Okouneff featuring the surnames Lieberman, Morgenstern, Tritsch, Wassertrilling, Wassing, Popper, Kohn and Janowsky; from Austria, Czechoslovakia and Russia (primarily of Jewish origin). |
| Olano Family: Ancestral heritage presented by Cristino Jose Olano in English and Spanish. |
| Olds Family: Ancestral research featuring pedigree, photographs and resources. Includes the variants Oulds and Old. |
| Olive: Ancestral heritage of Fred Olive from AL, USA. |
| Oliver-Velez: Ancestors of Denise Roberts Oliver-Velez including the surnames Oliver, Velez, Roberts, Weaver, Williams, Bodine, and Bratt. |
| Olley: Family history including associated lineages, message board and photographs. |
| Ollis: Multinational family histories pertaining to the name Ollis including photographs, memorials, vital records and lineages during War. |
| Oord: Researching the family lines of the Netherlands and Germany. |
| Oppersma Family Tree: Ancestral research including the surnames Cleworth, Davies, Edinburgh and Reedy. |
| Orange Family: Researching the lineage of Louiss Orange who arrived with wife and child in James Town, Virginia, USA on July 31st 1700. |
| Orear: Communication and information forum for O'Rears and Orears. |
| Orlovac: Descendants of Nikola Orlovac and Potomci od Nikole Orlovac including the lineages of Golub, Barisic and Lukenda from Bukovica. Compiled by Marinko Orlovac. |
| Orrell Family Association: Research repository for Orrell and variations, worldwide and all time periods. |
| Orta Family: Ancestral heritage of Robert G. Orta including the surnames Orta, DeOrta, Holcomb and Noriega. |
| Orton Archive: Historical data, will abstracts, deeds and parish register entries relating to Reginald Orton 1810-1862. Includes British ancestors, Inman of Nidderdale, Bayles of Laxton, Peirse of Bedale, Wastell of Scorton and Hutton of Marske. Compiled by Nancy McLaughlin. |
| Orzell: Researching the family lines from Galicia to Connecticut and Vermont and throughout the USA. |
| Osburn Family History: Ancestral heritage including the surnames Osburn, Bollinger, Burt and Sharp. |
| Oshel: History, pedigree and application of the name. |
| Ossowski: Search: Seeking information on Semyon Ionov Ossowski's relatives and those connected to the family blood line. Compiled by Alex Ossowski. |
| Oster: Ancestors and descendants of Joseph Hickman Oster and Henrietta Marie Galliano as compiled by Brian Joseph Oster. Features the surnames Oster, Hickman, Galiano, Ledet and Kennedy. Includes abstracts of Missouri marriages and Louisiana obituaries. |
| Ottolenghi: All family members regardless of country and relation. Includes spelling variants of Ottolenghi and Ottolangui. |
| Oudersluys: Family history and associated links including information on the Oudersluys Foundation. |
| Ouimet: Claude's Place: Family history featuring the surnames Ouiment, Proulx, Leclerc, Leclair and Théoret. |
| Overcast Family: Ancestral heritage of Louis Overcast including associated lineages and links. |
| Overhof(f) Family-tree: Contains over 3000 Overhof(f)'s/Oberhof(f)'s from all over the world (mainly USA, Germany, Austria and the Netherlands). Some branches of the family-tree date from before 1600 until now. |
| Oxman: Worldwide single name study. |
Classical
