There are 15 US Post Offices in Sullivan County serving a total of 41,090 residents equating to 2,739 residents per post office. It's estimated that approximately 65,584 packages are handled across the 15 county post offices annually. Sullivan County is a county located in the U.S. state of New Hampshire. As of the 2010 census, the population was 43,742, making it the second-least populous county in New Hampshire. Its county seat is Newport. Sullivan County is included in the Claremont-Lebanon, NH-VT Micropolitan Statistical Area."