There are 18 US Post Offices in Franklin County serving a total of 96,667 residents equating to 5,370 residents per post office. It's estimated that approximately 154,291 packages are handled across the 18 county post offices annually. Franklin County is a county located in the U.S. state of Missouri. As of the 2010 census, the population was 101,492. Its county seat is Union. The county was organized in 1818 and is named after Founding Father Benjamin Franklin. Franklin County is part of the St. Louis, MO-IL Metropolitan Statistical Area and contains many of the city's exurbs. It is located along the south side of the Missouri River. The county has wineries that are included in the Hermann AVA (American Viticultural Area) and is part of the region known as the Missouri Rhineland, which extends on both sides of the Missouri River."