There are 7 US Post Offices in Knox County serving a total of 9,039 residents equating to 1,291 residents per post office. It's estimated that approximately 14,427 packages are handled across the 7 county post offices annually. Knox County is a county in the U.S. state of Nebraska. As of the 2010 census, the population was 8,701. Its county seat is Center. In the Nebraska license plate system, Knox County is represented by the prefix 12 (it had the 12th-largest number of vehicles registered in the county when the license plate system was established in 1922)."