Derby is a city and unitary authority area on the River Derwent in Derbyshire, England. The county is named after Derby, which was its original county town. As a unitary authority, Derby is administratively independent from Derbyshire County Council. The population of Derby is 261,136.The Romans established the town of Derventio, which was later captured by the Anglo-Saxons and then by the Vikings who made Djúra-bý one of the Five Boroughs of the Danelaw.