Harrison County is a county on the eastern border of the U.S. state of Texas. As of the 2020 United States census, its population was 68,839. 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. Developed for cotton plantations by planters from the South, this county had the highest number of enslaved African Americans in Texas before the Civil War. They comprised 59% of the population.