Upshur County is a county located in the eastern part of the U.S. state of Texas. As of the 2020 census, the population was 40,892. The county seat is Gilmer. The county is named for Abel P. Upshur, who was U.S. Secretary of State during President John Tyler's administration. Upshur County is part of the Longview, Texas Metropolitan Statistical Area, as well as the Longview–Marshall, TX Combined Statistical Area.