Cosby is an uncommon given name of American origin, derived from the surname Cosby which has Norman roots. The surname is believed to have been brought to England by William de Coseboe, who accompanied William the Conqueror during the Norman conquest in 1066. It was later anglicized to Cosby and used as a given name, though its usage remains limited.
"Cosby is a rare name with only 23 recorded births over four years between 1908 and 1923."