1) People who work or live at night, sleeping during the day. 1957: "Night people, the professor and his wife used to retire at about 2:30 or 3 a.m." Fern Marja, "Black Coffee, Textbooks and TV." N.Y. Post, Sept 29, M4.
2) Nonconformists, Pop. By N.Y. City disc jockey and social commentator Jean Shepherd, c 1956.