In the first through fifth era, the story takes place in the country of Eos. Eos was devoid of normal animals besides for birds and bunnies. This is because the Hallow and Corruption caused the animals to leave the region for a more natural location. Animals that chose to stay were either killed by the denizens of Eos, or turned into horrific Soul Eaters in the corruption. In the middle of Eos stood the Rule Tower, with the laws of the country. It was built for the two deities; Razeil and Deavii.
Eos is now completely flooded, and thus destroyed. The survivors moved to The County of Dya.
To the west of the rule tower grew the Corruption. The Corruption was the home of the corrupt Demons. The landscape was twisted and ruined by the taint. The Corruption fed on the demonic energy coming from the Shadow Orbs that were in the chasms below.
Standing tall, there was a Demonic Fortress in the center of their lands. The first built by the Son of Lucifer was originally called Ebonlair. It's since changed it's name throughout the eras of the land.
To the east, of the rule tower grew the Hallow. The Hallow was the home of the hallowed Angels. The superficial dream-like landscape of the Hallow was overly bright. The water became Holy Water after the prolounged exposure. Some say that the Hallow's origins were related to the Hallowed Crystals.
Unlike the Corruption, the Angels typically built expansive cities in their lands. An example of this is Lucem, the city from the Fifth Era. Like the Demonic Fortresses, the Angel Cities changed their names.