I can’t comment on current continuity, but in his previous Earth-One and New Earth incarnations he was originally based in Colorado. The real Det. John Jones died and J’onn assumed his identity. IIRC, Erdel was originally in a small town but J’onn was based in Denver. As Martian Manhunter became a more public hero and joined the JL, he saw a lot more of the world and moved wherever the league took him. In NE he had many identities based in different places around the world. His actual Martian home was brought to Earth as a gift from Hal Jordan Spectre and resides in the Gobi desert, Mongolia.
