During the 2350s, Galen IV was disputed between the Federation and Talarians, who saw the Federation as encroaching on their territory. In 2357, the planet was attacked by Talarian forces, commanded by Endar. All the colonists were believed to have been massacred, the colony destroyed, but a single survivor emerged years later as Endar's adopted son Jono. (TNG: "Suddenly Human")
According to the Star Trek: Star Charts (pg. 37, "United Federation of Planets I", "United Federation of Planets II"), the Galen system was located in or near Federation space, in the Alpha Quadrant. This was a single star system. Galen was a K class star with a magnitude of +5, which was the same brightness as Sol. Galen IV was listed as a member planet of the Federation in 2378.