The Breakfast Kingdom first appears in the episode "Hitman." It is ruled by Breakfast Princess, Toast Princess, and Strudel Princess and is inhabited by Breakfast People. It appears to be located in the Desert of Doom. In "We Fixed a Truck," it returns with a slightly altered look. Finn, Jake, BMO, and Banana Man visit the kingdom's spa to take some of the grease from the deep fryer to make biodiesel. The kingdom returns in "Princess Day" to host the Princess Day event.
In "Hitman," the Breakfast Kingdom consists of Breakfast Castle and its surrounding environment. The castle appears to be situated at the end of a canyon. The castle itself consists of a large coffee percolator which sits on top of a dish. The dish is in turn sitting on top of pieces of coffee cake which sit on a foundation of fried eggs. The drain pipes in the canyon walls and the percolator are spewing coffee to make a moat around the castle which is crossed by several bridges made of bacon. In "We Fixed a Truck," the kingdom has a spa attached to the castle. A large, white cup and saucer are on the roof, and above the entrance, there is a bread-shaped sign with the word "SPA."
In "Hitman" and "We Fixed a Truck," a trailer and a dump truck are seen atop the rim of the canyon the castle is situated in. Both are comparable to things which would be seen at a real-world construction site and do not appear to be decayed to any degree. There are rocks stacked around the area, resembling the stone structures at real-world location Stonehenge. Mountains shrouded in clouds and more rock structures are seen in the distance.
Breakfast Princess and Toast Princess' room's walls are blue and the flooring has hot pink, pale pink, and white tiles. Oranges grow all around the room, some squirting juice into large glasses. The princesses' bed is orange and contains yellow pillows, a chicken feathered blanket, and chicken legs as bed legs, with eggs on top of them. There is a picture of a hen above their bed. Their phone is made of toast and the buttons are made of butter. The door is a chicken coop door. Next to the door, there is a drawer with a bell and what looks like cake on top of the drawer. The room also contains a cooked egg rug and one brown window.
The spa has a deep fryer that Breakfast People can relax in like a hot tub. The floor consists of large sunny-side up eggs, and the walls of the spa are made of sausages. Tall glasses of orange juice stand next to huge five-tier stacks of pancakes topped with melting pats of butter.
In "Princess Day," the kingdom looks very different. The castle is at least twice as tall, and its walls consist of bacon and stacks of pancakes instead of sausages. A bridge of bacon spans the pond created from the fountain of coffee issuing from the main percolator. A forest of orange trees surrounds the kingdom, in the midst of which is an oversize toaster.
- The Candy Kingdom, Breakfast Kingdom, the Wildberry Kingdom, and the Duchy of Nuts have edible citizens. In the case of the Candy Kingdom and Breakfast Kingdom, parts of the kingdom and its people may be consumed.
- So far, this is the only kingdom known to have more than one ruling princess at one time, as the Slime Kingdom has two princesses, Slime Princess and Blargetha, but only Slime Princess is ruling it.
- In "Jake the Dad," there was a bag shown from the Breakfast Kingdom Public Library, though there has been no other mention of it.