

The surname appears to have radiated out from the North of England, being particularly common in the North and West Ridings of Yorkshire and the county of Durham.
From the "Background" tab of FamilyTreeDNA's "Hamby/Hanby" group:
The first well recorded Hamby used as a surname was Walter de Hamby, who lived from approximately 1115[??]-1160 and was probably the same person as Walter fitz Roger recorded in 1115-1118. The name was variously spelled Hambia, Hunbia, Humbia and Hambi in Latin documents from the period. Walter fitz Roger's Domesday predecessor as lord of Hamby in England was a man named Wimund, though the precise relation between Walter and Wimund or Wimund and Roger is currently unknown. The name Wimund was found in both England and Normandy at the time of the conquest. It is Nordic in origin and is a form of the Old Norse name Vemundr.