It was created and ruled by Shirley in The Jerkinators!. He sucked up people and places from both Dimmsdale and Retroville to create a new realm of both places combined to live with all of his "friends". However, the creation of RetroDimmsdaleville would lead to the eventual destruction of the worlds both previous towns came from.
The world is completely 2D, with all people and objects being completely flat. The ground and sky are all pure white and completely flat extending in all directions.