(covers information from several alternate timelines)
Deneva, also known as Deneva Prime, was the prime planet in the Deneva system. Hosting the Deneva colony and Deneva Station, this Human-inhabited planet was considered one of the most beautiful worlds in the galaxy.
The Deneva colony was established on this planet in the mid-22nd century, originally as a freighting-line base in the area. Supplies would be sent to the miners in the system's asteroid belt and what was mined in the asteroids would be sent back to Deneva for transfer to other Earth, and later Federation, worlds and colonies. In 2267, there were over a million inhabitants on this world, with more than a hundred thousand living in the capital city alone. The nearest starbase was Starbase 10. (TOS: "Operation -- Annihilate!"; ENT: "Horizon", "Rogue Planet")
In late 2266 – eight months before the visit of the USS Enterprise – space vessels from Ingraham B brought an infestation of flying parasites. These parasites would have wiped out the colony, as they had Ingraham B and at least three other civilized worlds, had not Captain Kirk and his crew destroyed them. Many people died from the infestation, including Kirk's brother Sam, just before the arrival of the Enterprise, and his wife Aurelan, soon after. The couple had moved to the planet with their son Peter not long before the infestation. (TOS: "Operation -- Annihilate!")
Dr. Gabrielle Burnham's mission logs from a future timeline, viewed by Michael Burnham in 2257, listed Deneva among the devastated worlds where Control had wiped out all life by the 33rd century. (DIS: "Perpetual Infinity")
This planet's quadrant of origin is inferred based on the location of its primary from the Star Trek: Discovery episode "Magic to Make the Sanest Man Go Mad" and the Star Trek: Picard episode "Maps and Legends".
The city exteriors for Deneva were shot on location at the TRW Space and Defense Park in Redondo Beach, near Los Angeles. Filming took place on Wednesday 15 February 1967. The establishing shot of Kirk's brother's lab was a building on the campus of UCLA, and the entrance to the building was the cafeteria at TRW. (Star Trek Encyclopedia (4th ed., vol. 1, p. 202)) (These Are the Voyages: TOS Season One)
According to Star Trek: Star Charts (pp. 36, 45, "United Federation of Planets I") and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), in 2120, Zefram Cochrane visited this planet on his final voyage. In the mid-22nd century, Deneva was a destination on a Vulcan trade route. In 2378, Deneva was a Federation member.
Star Trek: Star Charts places Deneva in the Kappa Fornacis system. The novel A Choice of Futures identifies Deneva as Kappa Fornacis III. The novel mentions that Deneva was conquered by the Romulans twice during the Earth-Romulan War. The first time, the Romulans massacred the entire population. The planet was resettled after it was retaken by Earth forces, but the new colonists had to be evacuated after it was conquered again, three years later. The remaining colonists went into hiding in the asteroid mines and fought a guerilla campaign against the Romulans.