There are 10 US Post Offices in Greene County serving a total of 14,302 residents equating to 1,430 residents per post office. It's estimated that approximately 22,828 packages are handled across the 10 county post offices annually. Greene County is a county located in the U.S. state of Illinois. According to the 2010 census, it has a population of 13,886. Its county seat is Carrollton. It has a notable archaeological area known as the Koster Site, at which evidence of more than 7,000 years of human habitation has been excavated. Exhibits of artifacts from the site are displayed at the Center for American Archeology in Kampsville, Illinois."