Farmworld is an alternate timeline created when Finn wished that "the Lich never even ever existed" in the episode "Finn the Human". For this to have happened, the mushroom bomb would have had to not go off. In the alternate timeline created by this wish, Simon Petrikov froze the bomb, which crushed and killed Simon.
All of the standard timeline's events prior to the Mushroom War occurred, as signified by the existence of pre-War objects like the Enchiridion, and two known survivors of the war: Simon Petrikov (who would become the Ice King in Ooo's timeline) and Marceline. However, during the Mushroom War, a major deviation occurred that changed history.
During an attack where a massive mutagenic bomb, containing a green substance connected to the Lich, was dropped upon Earth, Petrikov used the power from his ice crown to create a vortex that catches the bomb and freezes it mid-flight, crushing him in the process. With his death, the ice power within him raged at the loss of its owner, and froze Earth into a pseudo-cryogenic state for 400 years.
Humanity remained the dominant species of the world and various environments continued to exist, including farms and arid areas. Some 600 years after the new Ice Age destroyed civilization, humanity has returned to a more or less medieval level of technology. Humans had achieved some technological advancement, such as the development of prosthetic limbs that can be used as weaponry.
Magic is known as to not presently exist in this world. The ice crown remained dormant from not being used, and Marceline chose to stay underground to protect the crown and the undetonated bomb, and never became a vampire, which would have stopped her aging process as it did in the original timeline. Some of the residents of Ooo would still exist as Humans, like Choose Bruce and Bobby, who exist as Choose Goose and Billy in the original timeline, due to the mutation of their respective ancestors.
- The Humans of Farmworld look different than those seen in the standard timeline. They have more detailed eyes (white circles with black pupils) rather than just black dots and visible noses.
- However, some of the Humans seen in Islands were shown to have visible noses but all seem to have black dot eyes (but have more detailed eyes in close ups).
- After Jake changed the Lich's wish in "Jake the Dog", it was unknown what happened to the Farmworld dimension. However, in "Crossover", it was revealed that the dimension still exists for unknown reasons.
- In the original storyboard for "Crossover", it was briefly explained by Prismo that since Jake was still in the Time Room when Finn left, the result in changing The Lich's wish led to Finn's consciousness splitting into two realities. In other words, a paradox was created because Jake remembered the original Finn while Finn also existed in a wish-altered state in Farmworld. Therefore, Finn was returned to the prime universe, but Farmworld continued to exist due to the aforementioned paradox.