Located in ZZ9 Plural Z Alpha.
Trillian spun her seat round to face him and shrugged.
“Just a couple of guys we seem to have picked up in open space,” she said. “Section ZZ9 Plural Z Alpha.”
The Hitchhiker's Guide to the Galaxy, Chapter 11
Although the primitive ape-descended denizens of this planet did not realize it, the Earth was designed by a supercomputer called Deep Thought, and was built by the Magratheans. Slartibartfast won an award for his fjords on the coast of Norway.
The Earth was actually a computer so vast that organic life became part of it's matrix.
IIt was destroyed by the Vogons five minutes before the completion of its program.