The name “Cayley” comes from a village called Cailly in Normandy, and the first members of the family to settle in England came with the Norman invasion of 1066. Over the next two centuries they acquired estates in East Anglia, Sussex, Gloucestershire and Yorkshire. By Tudor times the surname had evolved from "de Cailly" to "Cayley". Eventually the main branch settled in Yorkshire at a village called Brompton, inland from Scarborough. Since then the family has spread, and members are to be found in various English counties, Australia, Canada, New Zealand, the USA and elsewhere.
There are a number of Cayleys not clearly linked to the Brompton Cayleys. It is possible that some descend from members of the family who stayed in East Anglia or Sussex in the Middle Ages. The same may be true for some "Caley" families - this is a surname associated with East Anglia. A number of families varied the spelling of their surname between "Caley" and "Cayley".
Medieval records suggest that some families with the surname Callaway, Kellaway (or other variants) may have descended from a branch of the de Cailly family, but this is not definitively proven.
Census and other information implies that in the 19th century a few Irish immigrants to England and North America with surnames Kelly or Cawley changed them to Cayley.