Especially common as an African-American and Black-British name. The reasons for its popularity are not clear. It may well be a transferred use of the English surname Corey, which is derived from the Old Norse personal name Kori.
English: habitational name from any of various places called Carleton or Carlton, from Old Norse karl ‘common man’, ‘peasant’ + Old English tūn ‘settlement’ (compare Charlton 1). Places spelled Carl(e)ton (as opposed to Charlton) are in areas of Scandinavian settlement, mostly in northern England.