There are 5 US Post Offices in Decatur County serving a total of 26,495 residents equating to 5,299 residents per post office. It's estimated that approximately 42,289 packages are handled across the 5 county post offices annually. Decatur County is a county located in the U.S. state of Indiana. As of 2010, the population was 25,740. The county seat is Greensburg."