In Old English " ð " and " th " are the same
According to many on-line sources ð = th in old English, it comes from old Germanic alphabet, and was used by the Anglo-Saxon & the Norse.Not just in spelling, but in pronunciation.Thus is very likely Hildreds and Hildreths are or at least were the same family once upon a time.
However this has never been proven through genealogy or historical record.Although it could be proven by DNA testing.Today over two dozen Hildreths have proven through Y-DNA testing that their American ancestor who emigrated to America in 1635 shares a recent common ancestor with English Hildreth cousins whose ancestors never left England.
If you are a man or someone related to a man with the surname Hildred, and you have an interest in genealogy, I invite you to help us solve this mystery.Please contact me for information on how to have your Y-DNA tested, or join our DNA project at Family Tree DNA located at this website.
http://www.familytreedna.com/group-join.aspx?Group=Hildrethhttp://www.familytreedna.com/group-join.aspx?Group=Hildreth