By the mid-23rd century, Mantilles was the most remotely inhabited colony in the Federation, and was located at the edge of the Milky Way Galaxy. In the late 2260s, Mantilles had a population of 82 million people and was governed by former Starfleet officer, Robert Wesley.
In 2269, Mantilles was threatened with destruction by a cosmic cloud creature who wished to digest the planet. Governor Wesley's Starfleet training allowed him to maintain control of the population when they discovered their fates, and arranged for 5,000 children to be evacuated from the planet. Fortunately, the planet was saved by the crew of the USS Enterprise. (TAS episode & novelization: One of Our Planets is Missing)