(written from a Production point of view)
Aurelia was, according to the script of the Star Trek: The Animated Series episode "Yesteryear", a Federation member planet, and homeworld to the Aurelians. Neither Aurelia nor Aurelians were referred to in the final version of "Yesteryear".
Aurelia was in the list of member planets in the Star Trek: Star Charts. (United Federation of Planets I)
According to Star Trek Maps, Aurelia is the second planet in the Xi Herculis system.
According to The Worlds of the Federation, Aurelia is the fourth planet in the Xi Herculis system. It is called Meriabii by its natives.