Starbase 209 was a Federation starbase facility in Starfleet service in the 24th century, located somewhere in the galaxy's Alpha or Beta Quadrant.
History and specifics[]
In he year 2333, Admiral Mehdi ordered the USS Stargazer to abandon its survey mission to Beta Aurelia and head for the starbase. Once the starship arrived at the starbase, Captain Daithan Ruhalter and his crew were met by two descendants of the SS Valiant's crew and are informed of the Nuyyad's impending invasion of the galaxy. Soon after, the Stargazer left the base and headed for the edge of the galaxy to confront the Nuyyad. Following the successful conclusion of her mission, the Stargazer headed back to Starbase 209. (TNG novel: The Valiant)
The USS Enterprise-E docked at Starbase 209 for extensive repairs in early 2374, after being engaged in combat with several Cardassian and Dominion warships. Also undergoing repairs at the station at this time were the USS Gettysburg, the USS Earhart, the USS Seleya and the IKS Targ. (TNG - The Dominion War novels: Behind Enemy Lines, Tunnel Through the Stars)