Miller County is a county located in the southwestern corner of the U.S. state of Arkansas. It is part of the Texarkana, Texas - Texarkana, Arkansas, Metropolitan Statistical Area. As of 2000, the population was 40,443. The county seat is Texarkana. 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.

Additionally, Miller County is the first of the state's counties to be formed upon the creation of the Arkansas Territory.

The first five — Arkansas, Lawrence, Clark, Hempstead and Pulaski — were formed during Arkansas's days as part of the Missouri Territory. The county was abolished in 1838, and later recreated in December 1874 from a portion of neighboring Lafayette County. Despite its proximity to Texas (which has no state personal income tax), Miller County residents are not exempt from Arkansas's state personal income tax unless they reside within the city limits of Texarkana. .