Cognomen Килби (Kilby 
, Kilbi 
, Килби) , in all the world, is quite a common family name. The last name Килби is characteristic of Australia, where it is quite a rare surname, the United Kingdom, and New Zealand. Not in comparison with a country's population, it is the most numerous in the United States, the United Kingdom, and Australia. Very seldom, Килби is the forename as well as the last name.