There are 10 US Post Offices in Knox County serving a total of 38,192 residents equating to 3,819 residents per post office. It's estimated that approximately 60,959 packages are handled across the 10 county post offices annually. Knox County is a county located in Indiana in the United States. It was one of two original counties created in the old Northwest Territory in 1790 and was reduced to its present size in 1817. As of 2010, the population was 38,440. The county seat is Vincennes."