There are 3 US Post Offices in Caribou County serving a total of 6,920 residents equating to 2,307 residents per post office. It's estimated that approximately 11,045 packages are handled across the 3 county post offices annually. Caribou County is a county located in the U.S. state of Idaho. As of the 2010 Census the county had a population of 6,963. The county seat and largest city is Soda Springs."