Icor IX was the inhabited ninth planet in its system. In 2366, Jean-Luc Picard had given serious thought about attending a symposium on rogue star clusters at the Astrophysics Center on this planet. (TNG: "Captain's Holiday")

In 2371, the location of Icor IX was labeled in the star chart Data and Picard were studying in stellar cartography aboard the USS Enterprise-D. (Star Trek Generations, display graphic)

This planet was only mentioned in dialogue.
According to Star Trek: Star Charts ("United Federation of Planets"), in 2378, Icor IX was listed as a Federation member.