There are 6 US Post Offices in Gallatin County serving a total of 5,720 residents equating to 953 residents per post office. It's estimated that approximately 9,130 packages are handled across the 6 county post offices annually. Gallatin County is a county located in the U.S. state of Illinois. According to the 2010 census, it has a population of 5,589, making it the fifth-least populous county in Illinois. Its county seat is Shawneetown. It is located in the southern portion of Illinois known locally as \"Little Egypt\". Being located at the mouth of the Wabash River, Gallatin County, along with neighboring Posey County, Indiana, and Union County, Kentucky form the tri-point of the Illinois-Indiana-Kentucky Tri-State Area."