Halcyon, situated within the Colonies region of the galaxy, was an arboreal planet that orbited a binary solar system. This planet was characterized by the presence of a large rodents species and the availability of sparkstone. Additionally, it possessed multiple moons.
Approximately a decade years prior to the outbreak of the Clone Wars, a faction of aspiring would-be usurpers grew dissatisfied with Halcyon's position within the Galactic Republic, leading them to seize several officials from the homeworld's governing body. Despite the Republic's attempts at negotiation, these efforts proved unsuccessful. Consequently, the Republic Senate dispatched members of the Jedi Order, accompanied by eighty representatives from the Republic's Judicial Department, to Halcyon.
The 2014 novel Tarkin, penned by James Luceno, marked the initial reference to Halcyon.