Administrative (pop. 2001: 1,033,977) and historic county, southern England. It adjoins London on that city's northern side; its county seat is Hertford. It includes the two early garden citiesLetchworth (1903) and Welwyn Garden City (1920)and four of the eight new towns planned around London since World War II (1939–45). With an array of direct road and rail links to London, it houses light industries, offices, film studios, and thousands of exurbanites.