Acmetropolis is a huge city with futuristic styles and technology. It has it's own China Town, movie theaters, public pools, and jails. The Loonatics reside there at the large tower. It was subjected to attacks by the super-villains throughout the course of the show, most notably the comet being sent by Optimatus, the freezing from the Space Vikings' weapons, Paula Haynes/Weather Vane (with her attacks with lightning, a tornado, and Cloud Creatures), Dr. Dare, and various other villains.
In the year 2772 (the 28th Century), a meteor strikes the city planet of Acmetropolis, knocking it off its axis. This cosmic event releases supernatural forces unleashing a new kind of hero: The Loonatics.
In the episode The Comet Cometh, the city celebrating the one year anniversary of the Loonatics' debut, which means that it can be assumed that the episode and all future episodes take place in the year 2773. Additionally, a mysterious character, now known as Optimatus, debuts in the final moments of the episode. He states that the meteor's striking Acmetropolis in 2772 was not an incidental event but actually a deliberate attempt to destroy Acmetropolis. With the first attempt having the effects of the energy release and the Loonatics stopping a second attempt with a larger space rock in the episode, he states that he plans to attack the planet a third time. Later, in the two-part season-ending episode, "Acmegeddon," Optimatus returns and is revealed to be Zadavia's brother. He targets the Loonatics, Zadavia and all of Acmetropolis, hoping to destroy them all. They successfully save the world and send Optimatus to an unknown location in the galaxy via wormhole.
In season two, Acmetropolis gets shaken up by more chaos. In It Came From Outer Space, Rev and Lexi tamper with Tech's X3000 Automated Weapon System mistakening it for a video game, Melvin the Martian comes to Acmetropolis to destroy it after his spacecraft was hit by a missile from Tech's inventiion. Melvin threatens to shrink the planet, Lexi admits she tampered with Tech's invention and Melvin orders that Lexi be handed over to him in 24 Hours. Lexi then agrees to Melvin's demands and goes with Melvin to his spacecraft. After Melvin double crosses the team and starts srinking Acmetropolis anyway the Loonatics then stop him.
- Acmetropolis is an Ecumenopolis, there is only one "city" on the planet, and it covers the entire planet. It's never explained, though, how it appears to have only one of various major fixtures (zoo, power plant, reservoir, etc.).