Corvan II was the inhabited second planetoid in the Corvan system. This system, which was near the Aneto system, was located in the Beta Quadrant. Rainforests on the planetoid were home to the Corvan gilvo, which were threatened by industrial pollutants during the 24th century. (DIS: "The Butcher's Knife Cares Not for the Lamb's Cry", "Choose Your Pain"; TNG: "New Ground")
During the mid-23rd century, Corvan II was the site of a mining colony that produced forty percent of the Federation's dilithium supply. This made it strategically vital in the Federation-Klingon War, as half the fleet would be grounded without it. Because of this, a Starfleet blockade protected the colony.
Attack on Corvan II
Six months into the war, the Klingons ambushed the colony's blockade and destroyed its patrol ships. Several Klingon Birds-of-Prey bombarded the colony's magnetic shield, killing over two hundred colonists. By the time the colonists managed to send out a distress signal, the shield was projected to fail in six hours, while the closest Federation ship was eighty-four hours away.
Just after the shield failed and the colony had received a few direct hits, the USS Discovery used its unique spore drive to jump above the colony. The Discovery then destroyed the Klingon ships, saving the remaining colonists. (DIS: "The Butcher's Knife Cares Not for the Lamb's Cry")
According to reference work Star Trek: Star Charts ("United Federation of Planets I"), Corvan II was listed as a member planet of the Federation in 2378. The Star Trek Encyclopedia (4th ed., vol. 1, p. 163) also identified it as a Federation planet.