There are 5 US Post Offices in Alpena County serving a total of 50,699 residents equating to 10,140 residents per post office. It's estimated that approximately 80,921 packages are handled across the 5 county post offices annually. Alpena County is a county located in the U.S. state of Michigan. As of the 2010 census, the population was 29,598. The county seat is Alpena. It is considered to be part of Northern Michigan. Alpena County comprises the Alpena, MI Micropolitan Statistical Area."