town, Derbyshire Dales district, administrative and historic county of Derbyshire, England. It consists of a group of settlements extending along the River Derwent. Matlock is noted for its beautiful valleys and rugged hills. Between Cromford (site of Sir Richard Arkwright's first water-powered mill, 1771) and Matlock Bridge (16th century), the River Derwent runs through a narrow gorge. Matlock was once famous for its hydropathic treatment, but the largest establishment (1852) in the town now houses the county offices. Pop. (2001) 9,496.