The moon? Although that did belong to Earth in the first place....what about Neptune? There were some humans there, and the human-built Santa lives there.
When do we see humans living on Neptune? I'm actually inclined to believe that Neptune was colonized by an alien race with superior technology to Earth's, at least in terms of terraforming. I mean, it wasn't until the 27th century that Earth could terraform Mars, and that would have been a LOT easier than doing the same for a gas giant in the outer solar system.