Hatfield is a town and civil parish in Hertfordshire, England, in the borough of Welwyn Hatfield. It had a population of 29,616 in 2001, and is of Saxon origin. Hatfield House, the home of the Marquess of Salisbury, is the nucleus of the old town. From the 1930s when de Havilland opened a factory until the 1990s when British Aerospace closed, Hatfield was associated with aircraft design and manufacture, which employed more people than any other industry. Hatfield was one of the post-war New Towns built around London and has much modernist architecture from the period. The University of Hertfordshire is based there. Hatfield is 20 miles (30 kilometres) north of London. A train service runs directly from Hatfield Station to Kings Cross, taking approximately 20 minutes on the fast service.