The Deneva colony was one of the oldest Earth colonies, established prior to the 2150s on Deneva Prime as a freighting line base for mining in the sector's asteroid belt. In 2153, the ECS Horizon was en route to Deneva Station. (ENT: "Horizon")
In the 2260s, the planet had a population of just under a million, with over 100,000 people in the capital city alone.
In 2267, the colony was infested by neural parasites, killing several colonists, including George Samuel Kirk. The USS Enterprise investigated the situation, and Capt. James T. Kirk was forced to consider destroying the colony to stop the parasites' spread. However, a better solution was found; satellites were placed around the planet bathing it in ultraviolet light, destroying only the parasites. (TOS: "Operation -- Annihilate!")