There are 13 US Post Offices in Adams County serving a total of 80,671 residents equating to 6,205 residents per post office. It's estimated that approximately 128,760 packages are handled across the 13 county post offices annually. Adams County is the westernmost county of the U.S. state of Illinois. As of the 2010 census, the population was 67,103. Its county seat is Quincy. Adams County is part of the Quincy, IL\u2013MO Micropolitan Statistical Area."