Gregg County is a county located in the eastern part of the U.S. state of Texas. As of the 2010 census, its population was 121,730. Its county seat is Longview. The county is named for John Gregg, a Confederate general killed in action during the American Civil War.Gregg County is part of the Longview, TX Metropolitan Statistical Area as well as the Longview–Marshall, TX Combined Statistical Area.