town, Dacorum district, administrative and historic county of Hertfordshire, England, northwest of London. The first charter was granted in 1539. The new town, one of eight designed by British planners to accommodate London's overspill population, has been grafted onto the old market town since 1947. Landscaping has been assisted by the presence of the picturesque River Gade. Major new offices and papermaking, electrical, and light engineering industries have contributed to its rapid growth. Pop. (2001) 83,118.