In 2155, representatives from Tellar took part in talks on Earth to form a Coalition of Planets. In 2161, Tellar became a founding member of the United Federation of Planets. (ENT: "Demons", "Zero Hour")
Background information Edit
According to Star Trek: Star Charts, (pp. 19, 36, & 44) and the Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the Tellar (61 Cygni) system was located in the Tellar Sector (Sector 007), a region of space in the Alpha Quadrant. The system was a binary system of two K class stars. In the 22nd century, this system was a stop on the Earth trade routes.
According to the Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), Tellar was a planet orbiting Tellar A (61 Cygni A). The planet had two moons, named Kera and Phinda. Its official name was United Planets of Tellar Prime. Alternative names for this planet were Tellar Prime, Miracht, Pangeos V. Planet's capital was Shirgat. Tellarites were the primary species. In the late 24th century, the planet had a population of 2.3 billion. This planet was warp-capable in 1959.
The Worlds of the Federation reference book states Tellar to be the fifth planet of the 61 Cygni system. It also gives Miracht as an alternative name for the planet and lists two moons called Kehra and Phinda. (citation needed • edit)