Essex /ˈɛsɨks/ is a ceremonial and administrative county in England, and a home county north-east of London. It borders the counties of Suffolk and Cambridgeshire to the north, Hertfordshire to the west, Kent across the estuary of the River Thames to the south and London to the southwest. Essex County Council is the principal local authority for much of the county, sharing functions with 12 district and borough councils. The county town is Chelmsford. Essex is a region at the second level for European statistical purposes.

The Ceremonial County forming this region comprises three areas of local government: the two-tiered non-metropolitan county of Essex and the unitary authority areas of Thurrock and Southend-on-Sea.

The historic county can be considered the oldest as Wessex and Mercia were replaced for administration since before the Norman period and a vestige of the term Northumbria exists in Northumberland – Essex occupies the eastern portion of the pre-England Kingdom of Essex. Large swathes of the county which are closest to London are part of the Metropolitan Green Belt, which prohibits urban development in its green spaces. It is the location of the regionally significant Lakeside Shopping Centre and London Stansted Airport; and the new towns of Basildon and Harlow.