The Deneb system was an inhabited planetary star system in the Alpha Quadrant. The primary was named Deneb. There were four known planets in this system: Deneb II, Deneb IV, Deneb V, and Deneb XX. Its location in the Milky Way Galaxy was depicted on a Federation star chart in 2293. (TOS: "Where No Man Has Gone Before", "I, Mudd", "Wolf in the Fold"; Star Trek VI: The Undiscovered Country, production art; DS9: "Whispers") The system was located between Earth and Argelius II. (TOS: "Wolf in the Fold")
The system was home to the Denebians and the Bandi, and to animals including the Denebian slime devil and Denebian whale. (DS9: "A Man Alone", "The Nagus"; TAS: "The Ambergris Element")
History
Prior to 2265, James T. Kirk and Gary Mitchell had spent some time on Deneb IV. Gary Mitchell spent a night there with a woman he later described as "a nova," producing unspecified "after effects." He also communicated telepathically with some of the Deneb IV natives. (TOS: "Where No Man Has Gone Before")
Some time prior to 2267, the Redjac entity became a mass murderer of women on Deneb II. The entity was never caught and was only known by the name Kesla by the natives. (TOS: "Wolf in the Fold")
In 2267, Harry Mudd attempted to conn the Denebians on Deneb V. He was caught, but escaped the planet before his execution. (TOS: "I, Mudd") In 2270, the crew of the USS Enterprise represented the Federation at the dedication ceremonies for the new Academy of Science on the planet. (TAS: "The Pirates of Orion")
In 2364, the starship USS Enterprise-D visited Deneb IV to investigate the Farpoint Station. The native Bandi claimed it was built by them. The station was however discovered to be a spaceborne entity forced by the Bandi to take the shape of a space station. (TNG: "Encounter at Farpoint")
In 2370, the GHD Per'ot visited Deneb XX before arriving to Deep Space 9. (DS9: "Whispers")