In 2267, the USS Enterprise put in to Cygnet XIV for general repair and maintenance. During the overhaul, the planet's inhabitants, deciding that the ship's computer lacked sufficient personality, modified it with a female one. This caused some annoyance to the crew, especially Captain Kirk, whom the computer voice often addressed as "dear", and Mr. Spock, who noted that the computer had "an unfortunate tendency to giggle."
This planet was only mentioned in dialogue.
According to Star Trek: Star Charts ("United Federation of Planets I", "United Federation of Planets III") and the Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), Cygnet XIV was a Federation member by 2378. The Cygnet system was located in the Alpha Quadrant. The system's primary was a K-class star.