There are 4 US Post Offices in Niobrara County serving a total of 2,454 residents equating to 614 residents per post office. It's estimated that approximately 3,917 packages are handled across the 4 county post offices annually. Niobrara County is a county located in the U.S. state of Wyoming. As of the 2010 census, the population was 2,484, making it the least populous county in Wyoming. Its county seat is Lusk. It is west from the Nebraska-South Dakota state line."