"inhabitant of the southern part of a country," late 15c., variant (originally Scottish and northern English) of southren (late 14c.), on analogy of Briton, Saxon, from Old English suðerne or Old Norse suðrænn "southern" (see southern). Popularized in English by Jane Porter's enormously popular historical novel "Scottish Chiefs" (1810), and adopted in U.S. by many in the Southern states. She also used it as an adjective. Old English had suðmann "Southman."
But the moment I heard he was in arms, I grasped at the opportunity of avenging my country, and of trampling on the proud heart of the Southron villain who had dared to inflict disgrace upon the cheek of Roger Kirkpatrick. [Jane Porter, "Scottish Chiefs," 1809]