There are 7 US Post Offices in Montgomery County serving a total of 7,810 residents equating to 1,116 residents per post office. It's estimated that approximately 12,466 packages are handled across the 7 county post offices annually. Montgomery County is a county located in the U.S. state of Arkansas. As of the 2010 census, the population was 9,487. The county seat is Mount Ida. Montgomery County is Arkansas's 45th county, formed on December 9, 1842, and named after Richard Montgomery, an American Revolutionary War general.