Harrison County is a county on the eastern border of the U.S. state of Texas. As of the 2010 census, its population was 65,631. The county seat is Marshall. The county was created in 1839 and organized in 1842. It is named for Jonas Harrison, a lawyer and Texas revolutionary.Harrison County comprises the Marshall, TX Micropolitan Statistical Area, which is also included in the Longview–Marshall, TX Combined Statistical Area.