There are 2 US Post Offices in Gem County serving a total of 15,596 residents equating to 7,798 residents per post office. It's estimated that approximately 24,893 packages are handled across the 2 county post offices annually. Gem County is a county in the U.S. state of Idaho. As of the 2010 census, the population was 16,719. The county seat and largest city is Emmett. Gem County is part of the Boise, ID Metropolitan Statistical Area. Gem County is home to the Idaho ground squirrel."