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: habitational name from places called Merton in London, Devon, Norfolk, and Oxfordshire, named in Old English with mere ‘lake’, ‘pool’ + tūn ‘enclosure’, ‘settlement’. Compare Marton, Martin 2.