MacMahon
- Researching the Clan Mac Mahon of the Kingdom of Oriel. Includes the spelling variants of McMahon, Mahon, Mathews, McArdle and McPhillips. Features maps, illustrations, coat of arms and associated links.
- http://www.mcmahonsofmonaghan.org/

McMahon
- Bill McMahon's family database.
- http://worldconnect.rootsweb.com/cgi-bin/igm.cgi?db=:2678090

McMahon: My Family Tree
- Pedigree database as compiled by Kerry McMahon.
- http://worldconnect.rootsweb.com/cgi-bin/igm.cgi?db=:2311092

McMahon/Willette Family Tree
- Documenting the lineages of McMahon and Willette.
- http://worldconnect.rootsweb.com/cgi-bin/igm.cgi?db=:2089045

McMahon Family
- Descendants of Joseph McMahon as compiled by David Charles McMahon from Gambier, OH USA.
- http://familytreemaker.genealogy.com/users/m/c/m/David-C-Mcmahon/

McMahons of Emyvale
- Descendants of Peter McMahon and wife, Elizabeth McKenna of Monaghan, IRL.
- http://homepage.eircom.net/~mcmahon/

McMahon: Two Septs
- Researching the descendants of Mahon O'Brien of County Clare, a descendent of the Irish king Brian Boru; and the lineages of the Kingdom of Oriel, Ulster, the family of Conn and the rebel Colla da Crioch.
- http://homepage.mac.com/jmcmahon/TwoSepts/