They live in holes in the ground according to Google.
But do they live singly, in pairs, or towns like prairie dogs?
WikiAnswers said this: “Except for mother chipmunks with a litter, chipmunks live alone and will defend the area around their burrow.” While I’m not always confident of WikiAnswers’ validity, the discussion of chipmunk tunnels and nests on several other sites always used the singular, as if it were assumed we were talking one chipmunk per burrow. So I’m inclined to trust that answer.
Thanks!