There are 8 US Post Offices in Lyon County serving a total of 11,590 residents equating to 1,449 residents per post office. It's estimated that approximately 18,499 packages are handled across the 8 county post offices annually. Lyon County is the most northwesterly county of the U.S. state of Iowa. As of the 2010 census, the population was 11,581. The county seat is Rock Rapids. Lyon County is named in honor of Brigadier General Nathaniel Lyon, who served in the Mexican-American War and the Civil War. He was killed at the battle of Wilson's Creek, Missouri, on August 10, 1861, after which the county was named for him. The county's name was originally Buncombe County, but was changed by the state legislature on September 11, 1862."