town and borough (district), administrative and historic county of Hertfordshire, England, situated on the northwest periphery of London and on the Rivers Colne and Gade and on the Grand Union Canal. It is primarily a residential town for London commuters and a shopping and educational centre. The main industry is printing; there are also breweries, engineering, and chemical works. Area 8 square miles (21 square km). Pop. (2001) 79,729.