The Justice League was founded after seven heroes including Superman, Batman, Wonder Woman, Flash, Green Lantern (Hal Jordan), Aquaman and Martian Manhunter who had to work together to defeat an alien invasion.
They did not go public with their alliance at first. They were initially based in the Secret Sanctuary, a cave hollowed out in Mount Justice by Superman and Green Lantern. The League quickly expanded to ten members—Green Arrow, Hawkman and Hawkwoman had joined, the alliance went public shortly after.
After the alliance went public, several new members joined the group. A new hideout was chosen: the orbiting Watchtower satellite, although they also used the Hall of Justice as a front for tourists and the media.