Earth is the third planet from the Sun. The Teenage Mutant Ninja Turtles were born on Earth and currently dwell there. Some of the most important countries on the Earth in the Teenage Mutant Ninja Turtles stories are the United States of America and Japan. The main inhabitants on Earth are Humans.
In every incarnation of the Teenage Mutant Ninja Turtles, villains (mostly Shredder) are always trying to take over the Earth, resulting that the Turtles' have to stop them.
In the first 5 episodes, Shredder tried to conquer Earth with his army of Foot Soldiers and his mobile fortress the Technodrome. In the last of the five episodes the Turtles trap the Technodrome in Dimension X, along with Shredder, Krang, the Foot clan and Bebop and Rocksteady. Since then Shredder, with Krang's help, tried in every episode to get his Foot soldiers and the Technodrome out of Dimension X to finally conquer Earth, but the Turtles always foils their plans. In many episodes, Shredder tried to conquer Earth by other ways, but these plans are also foiled by the Turtles.
During the last two seasons, when Shredder and Krang were trapped in Dimension X for good, the alien warlord Lord Dregg tried to conquer Earth by manipulating the people, letting them believe that he is an hero who came to save them. The Turtles unmasked him and trapped him in Dimension X.
However, Shredder, Krang and Dregg were not the only ones, many villains tried to conquer Earth, but luckily the Turtles always stops them.
Ch'rell, the Utrom Shredder, who is known as the most dangerous creature in the galaxy, also tried to conquer Earth, but the Turtles always defeat him.