There are 14 US Post Offices in Montgomery County serving a total of 29,499 residents equating to 2,107 residents per post office. It's estimated that approximately 47,084 packages are handled across the 14 county post offices annually. Montgomery County is a county located in the U.S. state of Illinois. According to the 2010 census, it had a population of 30,104. Its county seat is Hillsboro."