Earth is the representation of our world within the series of Hataraku Mao-sama!, and the main setting of the story. It actually exists within the same universe in another galaxy from the magical world of Ente Isla, from which most of the main cast originates.
This Earth is very similar to Ente Isla in several regards, encompassing a variety of landscapes, settlements, oceans, and rivers. As the series version of the planet is modeled after the real world we live in, the majority of humans originating from Earth are not known to possess any type of special powers or abilities, a stark contrast to many of the human characters from Ente Isla who are capable of wielding magic. Most people do not believe in the supernatural and view such things as the stuff of fiction. As such, sources of magic are scarce on Earth, rendering demons and magicians unable to freely use their abilities without the risk of running out of power, as they would be left with no way to replenish it. As a result, visitors from Ente Isla must conserve their magical energy until they find alternative methods to replenish their power.
As the series version of Earth is based on our own, the geography is identical to that of its real-life namesake. Vast oceans cover the majority of the planet's surface; thus, the majority of the world's population lives scattered across the many islands and larger continents which comprise the world's landmass. The story is set in the Nation of Japan, a large archipelago resting off the coast of continental Asia.