There are 42 US Post Offices in Penobscot County serving a total of 143,639 residents equating to 3,420 residents per post office. It's estimated that approximately 229,264 packages are handled across the 42 county post offices annually. Penobscot County is a county located in the U.S. state of Maine. As of the 2010 census, the population was 153,923. Its county seat is Bangor. The county was established on 15 February 1816 from a portion of Hancock County when the area was still part of Massachusetts. Penobscot County comprises the Bangor, ME Metropolitan Statistical Area."