Miller County is a county located in the southwestern corner of the U.S. state of Arkansas. As of the 2020 census, the population was 42,600. The county seat is Texarkana. Miller County is part of the Texarkana, TX-AR, Metropolitan Statistical Area. When first formed, Miller County was Arkansas's sixth county, established on April 1, 1820, and named for James Miller, the first governor of the Arkansas Territory.