Hertfordshire (härˈfərdshĭr, härtˈ–) [key], county (1991 pop. 951,500), 631 sq mi (1,634 sq km), E central England. The county seat is Hertford, but Watford, Hemel Hempstead, Stevenage, and St. Albans are more important urban centers. Administratively, the county is divided into the districts of Three Rivers, Watford, Hertsmere, Welwyn Hatfield, Broxbourne, East Hertfordshire, Stevenage, North Hertfordshire, St. Albans, and Dacorum. The county contains four of the eight new towns planned around London since 1947: Hatfield, Hemel Hempstead, Stevenage, and Welwyn Garden City.
The terrain is level except for an extension of the Chiltern Hills in the northwest. The chief streams are the Colne, the Lea, and the Stort, which drain into the Thames. Although one of London's "Home Counties," Hertfordshire is primarily an agricultural region, producing large quantities of wheat and hay as well as dairy products, vegetables, and flowers for the nearby London market. There are diverse industries, such as brickmaking, printing, brewing (especially in Watford), papermaking, and engineering. The county figured prominently in the military history of England, particularly during the Wars of the Roses (see Roses, Wars of the).