61 Cygni was an inhabited binary star system consisting of the stars 61 Cygni A and 61 Cygni B. This system was located approximately eleven light years from the Sol system, part of the constellation Cygnus. The system was located in the Alpha Quadrant.
In 2364, the location of 61 Cygni was labeled on a star chart of the stellar neighborhood with Sol at the center. This chart was stored in the USS Enterprise-D library computer. Also that year, the chart was scanned by Outpost 63. (TNG: "The Naked Now", "The Last Outpost", "Conspiracy" production art)
In 2399, the location of 61 Cygni was labeled on a Federation star chart that was in Fleet Admiral Kirsten Clancy's office at Starfleet Headquarters. This system was in or near to Federation space. (PIC: "Maps and Legends")
This star system was only mentioned in writing.
The star chart naming stars within twenty light years of Sol was drawn by Rick Sternbach for the Star Trek Spaceflight Chronology (p. 77) in the late 1970s. This chart showed Earth commercial and exploration routes after the use of warp drive began. 61 Cygni was the destination on an exploration route.
According to Star Trek: Star Charts (pp. 18, 19, 36, 44, 56; "United Federation of Planets I") and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the two stars of 61 Cygni (Tellar) were K-class stars. Tellar Prime orbited 61 Cygni A. The system was located in Sector 007 (Tellar Sector).