From the Super Mario Wiki
The Mushroom Kingdom is the primary setting of the Mario franchise. It is ruled by Princess Peach and its appearance changes from game to game. Despite this, the kingdom consists of many similar recurring landscapes, such as plains, deserts, islands, forests, mountains, snowy areas, and volcanoes.
In Super Mario Bros. and the New Super Mario Bros. games, the Mushroom Kingdom is often portrayed as having eight differently-themed worlds (usually grasslands, desert, snow, etc.) that Mario has to travel through in order to rescue Peach from Bowser. Super Mario RPG: Legend of the Seven Stars is the first game to show civilian life in the Mushroom Kingdom, something continued later in games such as the Paper Mario and Mario & Luigi series. Mario Kart 64 and later Mario Kart games reveal that Mushroom Kingdom has metropolitan areas in the forms of Toad's Turnpike, Mushroom City and other urban courses.
In The Super Mario Bros. Super Show!, the Mushroom Kingdom, most commonly referred to as "Mushroomland", is a central plot point in the show; the Mushroom Kingdom is apparently under the influence of King Koopa in the show. Mario, Luigi, Toad and Princess Toadstool spend the bulk of the series' episodes searching for someone or something that could free it from his grasp.
Leaping Lizards describes the Mushroom Kingdom as being deep under the surface of the Earth, which is used as an explanation for how Mario and Luigi can reach the Kingdom through a series of pipes in Brooklyn.
The Mushroom Kingdom has inspired several stages in the Super Smash Bros. series. Two of these, both called Mushroom Kingdom, are based off of the kingdom as it appeared in the original Super Mario Bros., with usable Warp Pipes and POW Blocks in Super Smash Bros., and ? Blocks and Brick Blocks in Melee. Despite its name, Mushroom Kingdom II from Melee is based off of Subcon as it appeared in Super Mario Bros. 2. All three of these stages feature 3-D versions of stage elements, such as blocks and platforms, while any characters are portrayed as flat 2-D images.
In Super Smash Bros. Melee's Adventure Mode, the first stage is also called Mushroom Kingdom, where players have to get past Goombas, Koopa Troopas, and a team of Yoshis to reach Princess Peach's Castle, where Peach and either Mario or Luigi are fought. Two Toads also appear, one at the Yoshi arena and one at the endpoint.
Super Smash Bros. Brawl features Mushroomy Kingdom. This stage indicates that in the alternate world of Super Smash Bros., the Mushroom Kingdom was abandoned after Super Mario Bros. Familiar structures are now old, worn-down ruins and the entire stage appears as a barren desert and cave. The stage depicts replicated versions of either World 1-1 or World 1-2 when selected.
The Mushroom Kingdom appears as a mushroom-shaped island in Super Mario Odyssey, although smaller than its previous appearances.
The Mushroom Kingdom is a monarchy ruled by Princess Peach. The kingdom's capital is Toad Town. Here, Princess Peach resides in her castle. Early material also includes her father, the kindly Mushroom King, who is mentioned to rule alongside her. However, he does not seem to perform any administrative functions, and his presence is largely forgotten in the series.
Princess Peach keeps a hoard of Toad guards at her castle. However, Mario, Luigi, and many other heroes of the Mushroom Kingdom have fought to save it and its princess countless times before. Currently, Princess Peach staffs and supports Toad Houses in major towns near Toad Town.
The Mushroom Kingdom's population is very vast, consisting of hundreds of species. Most prevalent are Toads, Koopa Troopas, Goombas, Yoshis, and Boos. Even though Princess Peach, Mario, and Luigi are human, there are very few humans living in the Mushroom Kingdom.
The Mushroom Kingdom primarily uses coins for tender, referred to as Mushroom Coins in the Beanbean Kingdom. Coming in six varieties, coins are often found scattered throughout the Kingdom. The coin has undergone several changes throughout the years; the three most prominent coin designs are the blank design, the star design and the "|" design.
Below is a table detailing the value of each type of coin.
Cities, towns, and castles
Super Mario RPG: Legend of the Seven Stars
Paper Mario series
Mario & Luigi series
Mario Kart series
Names in other languages