There are 8 US Post Offices in Bay County serving a total of 103,656 residents equating to 12,957 residents per post office. It's estimated that approximately 165,447 packages are handled across the 8 county post offices annually. Bay County is a county in the U.S. state of Michigan. As of the 2010 census, the population was 107,771. The county seat is Bay City. Bay County comprises the Bay City, MI Metropolitan Statistical Area, which is included in the Saginaw-Midland-Bay City, MI Combined Statistical Area. It is also considered to be part of the Mid Michigan region."