Essex is a county in the east of England. It has a population of around 1,750,000 people. It is part of the East of England region. Chelmsford is the county town of Essex, as well as being its only city. Essex has London and Hertfordshire on its western border and the whole of the east of the county is coast-line. The north of the county borders Suffolk and Cambridgeshire. The south of the county is on the Thames Estuary. The Dartford Tunnel can be used to drive under the River Thames between Essex and Kent.