Harrison County was formed from Shelby County, created on January 28, 1839, and organized on June 12, 1842. It was named in honor of Jonas Harrison, a pioneer statesman of New Jersey who came to Texas in 1820, was a member of the First Convention of Texas held at San Felipe in 1832, and died in 1836. Marshall, the county seat, was named in honor of John Marshall, Chief Justice of the United States Supreme Court.