There is an exception: A small island nation called Chuka existed in ancient times, but it is unknown what became of the island.
Currently, there are six known "continents":
This is one of several "islands" large enough to be considered a continent. This is where much of the first season (from the time that the Searchers cross Heaven's Canyon until they leave the island on Horn's ship) and third season of the anime series takes place, and gameplay from Monster Rancher 2 and some of Monster Rancher 4 takes place here. It is home to the IMa organization, and also includes the small neighboring islands of Kawrea and Aurora (More than likely, this is the island where Genki begins his journey in both the first and third seasons).
This continent is mentioned in the anime series as the one that Durahan is currently taking control of. It can be seen on the map for Monster Rancher EVO far to the left and is a long peninsula much like the Northern continent.
This continent is long and treacherous, and is where part of the first season and all of the second season of the anime series is spent (after the Searchers cross over on Horn's ship). Gali, Naga and Gray Wolf all rule parts of this continent, and it is home to the FIMBA organization. Gameplay from Monster Rancher 1 and part of Monster Rancher 4 takes place on the lower end of the continent, while Monster Farm DS and Monster Rancher DS take place on the upper part.
This continent is only seen on the map in Monster Rancher EVO at the bottom of the earth. It is a large continent, ringed in jungles but frozen in the center.