Johnston Atoll is a 130 km² atoll in the North Pacific Ocean at
, about 1400 kilometers (750 nm) west of Hawaii. There are four islands located on the coral reef platform, two natural islands, Johnston Island and Sand Island, which have been expanded by coral dredging, as well as North Island (Akau) and East Island (Hikina), artificial islands formed from coral dredging.The four islands comprise a total land mass of 2.67 km². Due to the atoll's tilt, much of the reef on the southeast portion has subsided. But even though it does not have an encircling reef crest, the reef crest on the northwest portion of the atoll does provide for a shallow lagoon, with depths ranging from 3-10 m.
Johnston is an unincorporated territory of the United States, administered by the U.S. Fish and Wildlife Service of the Department of the Interior as part of the United States Pacific Island Wildlife Refuges. For statistical purposes, Johnston Atoll is grouped as one of the United States Minor Outlying Islands.
Its climate is tropical but generally dry. Northeast trade winds are consistent and there is little seasonal temperature variation. With elevation ranging from sea level to 5 m at Summit Peak, the islands contain some low-growing vegetation on mostly flat terrain and no natural fresh water resources.