When I first posted about my ancestory Stephen Diggedon, I overlooked one vital clue. In early census records, some of his children claimed Irish heritage (although later they listed themselves as English).
According to Michelle Deedigan (posting on GenForum), other variations of the name include Deedigan, Deighidan or Deegidan (added to previously known variations Diggadon, Diggdon and Digdon, all sometimes ending in "en" rather than "on").
In the same message thread, Maureen Borwick adds the following variations: Deggidan, Digaden, Degidan, Degidon, Digodan, Digidan,
Degiden and 0'Duigeadain (the original Gaelic spelling).
If you're researching any of these variations, please consider joining the Digdon mailing list at Rootsweb.