Decos Prime was the inhabited prime planet in its star system. This planet was located in the Alpha or Beta Quadrant. This Federation planet was the site of a Starfleet base, located less than a day and a half's journey from Deep Space 9.
In 2375, the Starfleet Chief of Operations at the base was Al Lorenzo. Lorenzo borrowed and returned Sisko's desk in the space of three days and agreed to provide an induction modulator as payment, in a series of trades organized by Nog to accelerate repairs of the USS Defiant. (DS9: "Treachery, Faith and the Great River")
This planet was only mentioned in dialogue.