Hillary Clinton Booked in Colorado

... well, overbooked is more like it.

Sources tell TMZ that Team Hillary had reserved hundreds of Denver hotel rooms for staffers and supporters during the Democratic National Convention in August -- rooms they really won't be needing anymore!

Now, we're told the campaign has sent emails to politicos, charity organizers and supporters who might be looking for a place to stay for the big bash!

Calls to Hillary's camp have not yet been returned.