The On a Cob Planet is a distant planet in the Milky Way Galaxy that looks very similar to Earth. It appeared in the episode The Wedding Squanchers, where The Smith Family moved, having to stay away from Federal Jurisdiction. On this planet, everything is on a cob, even mountains, down to the atomic level. When Rick realized this, he was visibly disturbed, hauling the family off of the planet as quickly as possible.
The show's creators joked that there will be a three episode arc in Season 3 exploring the origin of the 'cob', and Rick's history and relationship to it.