Custer County is a county in the U.S. state of Nebraska. As of the 2010 census, the population was 10,939. Its county seat is Broken Bow. The county was formed in 1877 and named after General George Armstrong Custer, who was killed at the Battle of Little Bighorn. In the Nebraska license plate system, Custer County is represented by the prefix 4 (it had the fourth-largest number of vehicles registered in the county when the license plate system was established in 1922).