Essex, administrative, geographic, and historic county of eastern England. It extends along the North Sea coastline between the Thames and Stour estuaries. The administrative county covers an area within the larger geographic county, which in turn covers a part of the original historic county of Essex. The administrative county comprises 12 districts: Basildon, Braintree, Epping Forest, Harlow, Maldon, Rochford, Tendring, Uttlesford, and the boroughs of Brentwood, Castle Point, Chelmsford, and Colchester. Chelmsford, centrally situated, has long been the county headquarters and is also the seat of a church diocese.