Gregg County is part of the Longview, Texas Metropolitan Statistical Area and the Longview–Marshall, Texas combined statistical area. Discovery of oil near Kilgore, Texas, in October 1930 was the beginning of an oil boom that attracted workers to the county and expanded the population by more than 500% by 1940, according to the census. By that time, the economy had stabilized but the East Texas Oil Field, extending in five counties, has continued to be important to the county and region's economy.