|Affiliation:||United Federation of Planets|
Marcos XII was an inhabited planet. It was the twelfth planet in the Marcos planetary system. The system was located in the Alpha Quadrant. The planet was affiliated with the United Federation of Planets. The nearest starbase was Starbase 4.
This planet was colonized by the Federation prior to 2268, and had a population of millions. It was the first planet which the evil angel-being Gorgan decided to conquer once he was set loose. Gorgan used the children of the Starnes Exploration Party to capture the Constitution-class starship USS Enterprise and was using the ship to go to there. Tommy Starnes had relatives on Marcos XII. (TOS: "And the Children Shall Lead")