The homeworld of the warp-capable Orions, Orion was an inhabited planet. The planet was located in the Orion sector, Alpha Quadrant. This planet was near to the route that a spacecraft would travel from Deep Space 9 to Earth. (TNG: "Conspiracy", display graphic; DS9: "Little Green Men")
Orion once harbored a highly advanced civilization whose history had drawn great interest from Federation historians and archaeologists alike. During the mid-23rd century, noted Federation archaeologist Doctor Roger Korby translated medical records from the Orion ruins that helped revolutionize modern immunization techniques and were required reading at Starfleet Academy. In 2269, through the assistance of the Guardian of Forever, Starfleet officers Captain James Kirk, Commander Spock and historian Lieutenant Erickson traveled to the dawn of Orion's civilization to view the planet's history unfold firsthand. (TOS: "What Are Little Girls Made Of?"; TAS: "Yesteryear")
Devna, an Orion trapped in Elysia, told Kirk that she wished to return through the time barrier and see Orion again. Kirk offered to take her back with him, but she declined, stating that she had accepted where she now was in life. (TAS: "The Time Trap")
In 2293, the location of Orion in the Milky Way Galaxy was labeled in a star chart that was in Captain James T. Kirk's quarters aboard the USS Enterprise-A. (Star Trek VI: The Undiscovered Country, okudagram)
In 2372, Ferengi entrepreneur Quark attempted to smuggle kemocite on a highly-profitable side trip to Orion under the guise of taking his ship, Quark's Treasure, on a test flight to Earth. This proved to be unsuccessful due to sabotage. (DS9: "Little Green Men")
Further information Edit
According to Star Trek: Star Charts (pp. 36, 45, 60), the planet Orion was located in the Pi 3 Orionis system. This planet was visited by Zefram Cochrane on his final voyage in 2120. Orion was a non-aligned world before and after 2161, the founding date of the Federation. In 2378, Orion was a destination on the major space lanes.
In Star Trek Online, Orion Prime is the second planet in the Orion system, which has 5 worlds. It is also deserted due to excessive pollution.