Gregory Nunzio Corso was born on March 26, 1930, in New York City, New York, United States. He was the son of Fortunato Samuel and Michelina (Colonni) Corso.
His parents were in their teens when Gregory was born. A year after his birth, Corso's parents separated, and a boy spent his early childhood in foster homes and orphanages. At the age of eleven, he went to live with his biological father, who had remarried.