North American: from the title originally adopted as a nickname parallel to Duke, King, etc. The title was used in England in Norman times as an equivalent of the French comte ‘count’ it is from Old English eorl ‘warrior, nobleman, prince’. In some cases the given name may have been taken from the surname Earl, which was originally either a nickname or a term denoting someone who worked in the household of an earl.
English (very common in England, especially in the south Midlands, and in Wales) and German (especially northwestern Germany): patronymic from the personal name Adam. In the U.S. this form has absorbed many patronymics and other derivatives of Adam in languages other than English. (For forms, see Hanks and Hodges 1988.)