There are 4 US Post Offices in Polk County serving a total of 4,853 residents equating to 1,213 residents per post office. It's estimated that approximately 7,746 packages are handled across the 4 county post offices annually. Polk County is a county located in the U.S. state of Nebraska. As of the 2010 census, the population was 5,406. Its county seat is Osceola. The county was formed in 1856 and later organized in 1870. It was named after President James K. Polk. In the Nebraska license plate system, Polk County is represented by the prefix 41 (it had the 41st-largest number of vehicles registered in the county when the license plate system was established in 1922)."