There are 10 US Post Offices in Calhoun County serving a total of 43,989 residents equating to 4,399 residents per post office. It's estimated that approximately 70,211 packages are handled across the 10 county post offices annually. Calhoun County is a county in the U.S. state of Michigan. As of the 2010 census, the population was 136,146. The county seat is Marshall. The county was established on October 19, 1829 and named after John C. Calhoun, who was at the time Vice President under Andrew Jackson, making it one of Michigan's Cabinet counties. County government was first organized March 6, 1833. Calhoun County comprises the Battle Creek, MI Metropolitan Statistical Area and is included in the Kalamazoo-Battle Creek-Portage, MI Combined Statistical Area."