[NI1735]
from A Dictionary of English Surnames by P. H. Reaney (Routledge, London and New York) p. 418
"Southey; Peter de Suthag' 1219 AssY; John Ofthesuthhey 1315 FFEss; Sara Bysoutheya 1330 PND 613; Christopher Southey 1642 PrD. From Southey in Culmstock (Devon), Southey Green (Essex), Southey Wood in Ufford (Northants), or Southey in Ecclesfield (WRYorks)."