From the Super Mario Wiki
Hollywood is a city (actually, a district of Los Angeles, CA) on Earth, and is located in the United States. Countless movies and television shows are filmed either in or around Hollywood, making the city synonymous with the film industry. Highlights of Hollywood include the Hollywood Sign, which consists of giant white letters spelling out the name of the city atop a nearby hill, and the Walk of Fame, a sidewalk where celebrities are honored.
Hollywood was featured in The Adventures of Super Mario Bros. 3 episode "Dadzilla". Big Mouth and Kootie Pie Koopa, fed up with the way that their father was treating them at home, concluded that they had likely been adopted, and that their real father was a movie star living in Hollywood. The two Koopalings traveled to Hollywood on the Doomship via a Warp Pipe, but not without getting the attention of Mario and his friends.
In Hollywood, Big Mouth and Kootie Pie met up the giant robot, Madzilla, whom they presumed was their "real" father. Using their Magic Scepters, the Koopalings brought Madzilla to life, and fooled him into thinking that he was their father. With Dadzilla wrapped around their fingers, Big Mouth and Kootie Pie were free to terrorize Hollywood.
Eventually, Mario and his friends scared Big Mouth and Kootie Pie out of Hollywood with their own robot, Madzilla's Mom. With the Koopas gone, Hollywood was safe from their tyranny. Princess Toadstool then invited Dadzilla to live in Giant Land, as Hollywood was no place for a dinosaur like himself to live.