Starbase 201 was a Starfleet facility in operation in the mid-24th century. It is roughly around sixteen hours from Deep Space 9 for Starfleet ships.
Starbase 201 was the command post of Starfleet's Eighth Fleet during the late 2360s and 2370s. Admiral Ankora was the fleet's commanding officer. (Last Unicorn RPG module: The Price of Freedom)
In 2371, a Jem'Hadar child was to have been transferred from Deep Space 9 to Starbase 201 for study. (DS9 episode: "The Abandoned")
A year later, Benjamin Sisko brought the USS Defiant to Starbase 201 to meet with Admiral Dulev and her aide Colfax. (DS9 novel: The Heart of the Warrior)
On stardate 48607.0, the Vilossia Twilight, an Alpha Centaurian freighter, was hired by Quark to deliver a glerint of self-sealing stembolts to Starbase 201. The cargo, however, had been transferred to a different ship in error. (DS9 short story: "Infinite Bureaucracy")