There are 7 US Post Offices in Greene County serving a total of 9,290 residents equating to 1,327 residents per post office. It's estimated that approximately 14,828 packages are handled across the 7 county post offices annually. Greene County is a county located in the U.S. state of Iowa. As of the 2010 census, the population was 9,336. The county seat is Jefferson. The county is named in honor of General Nathanael Greene."