Northey Island is an island in the estuary of the River Blackwater, Essex. It is linked to the south bank of the river by a causeway, covered for two hours either side of high tide. The island is approximately 2km to the east of Maldon, Essex and 2km to the west of Osea Island.
The whole island and part of the bank near the causeway are now a Nature Reserve. It is uninhabited apart from the warden.
The Battle of Maldon, 991 is believed to have taken place on the south bank near the island.