There are 4 US Post Offices in Summit County serving a total of 20,992 residents equating to 5,248 residents per post office. It's estimated that approximately 33,506 packages are handled across the 4 county post offices annually. Summit County is one of the 64 counties in the U.S. state of Colorado. As of the 2010 census, the population was 27,994. The county seat is Breckenridge. Summit County comprises the Breckenridge, CO Micropolitan Statistical Area."