The Fire Kingdom is home to most of the Fire Elementals of Ooo. It is made up of volcanoes and seas of lava. Its monarchy lives in the Fire Palace. The Fire Kingdom made its first official appearance in "Thank You" and was a major location in "Incendium."
It first appears in "Evicted!" in a flashback that shows Marceline hula-hooping in a sea of flames. It's possible that the Fire Count ruled the land in the past, a flashback in "His Hero" shows him wearing a crown in what is appears to be the kingdom. Flame King currently rules the Fire Kingdom.
- Flame Lord
- Fire Wolves
- Flame Princess
- Lava Man
- Fire Count (formerly)
- Flame King
- Flame Jester (formerly)
- Flame Guards
- In "My Two Favorite People," Jake, Finn, and Lady Rainicorn have a picnic on what appears to be the border between the Grass Lands and the Fire Kingdom. This is also seen in the episode's title card.
- According to one map released with the original series pitch documents, the Fire Kingdom (or "Kingdom of Fire" as it's labeled on the map) is bordered by water and the Isle of Steam to the south. A different map calls the area the "Burning Lands" and contains the warning: "Do not go here. It's on FIRE!"
- In "His Hero," Billy is shown to have saved the Cotton Candy Princess from a possible Fire Kingdom inhabitant, the Fire Count, during "Billy's Song."
- The Fire Kingdom makes a major appearance in "Thank You"; it is revealed to be on the border with the Ice Kingdom, with all the ice and snow melting in the area between the two. Creatures such as Fire Wolves from the Fire Kingdom are found easily making their way into the Ice Kingdom as a result.
- In Incendium, Jake visits the Fire kingdom in hope of winning Flame princess to cheer Finn up. However flame princess showed her harsh side which caused Jake to reject her and she angrily chases him out of the Fire kingdom.
- It is said that the Fire Kingdom and Ice Kingdom border each other, but it is not visible on the Map of Ooo.