Board Thread:Spoilers!/@comment-26225812-20150618081046/@comment-24674051-20150702143331

If I recall the rumors correctly, Swan was the last name of the family that almost adopted her as a baby/infant. For whatever reason, that adoption was cancelled, but Emma was allowed to keep the name, since no one really knew her name. (and really, other than Emma, does she even have another name?).