Arthur County is a county located in the U.S. state of Nebraska. As of the 2020 United States Census, the population was 434, making it Nebraska's third least populous county and the seventh-least populous county in the United States (behind only Loving County, Texas; Kalawao County, Hawaii; King County, Texas; Kenedy County, Texas; McPherson County, Nebraska; and Blaine County, Nebraska). Its county seat and only incorporated community is Arthur.