Johnston Atoll is an uninhabited atoll in the North Pacific Ocean, located about 717 nautical miles west of Honolulu, Hawaii. It consists of four small islands, which together comprise an area of about 1,300 acres. The atoll is administered by the United States government as an unorganized, unincorporated territory.

The atoll was discovered in 1796 by an American sea captain, Joseph Pierpoint, and was claimed by the United States in 1858. During World War II, the atoll was used by the United States as a military base and airfield, and was the site of a major battle between American and Japanese forces in 1942. After the war, the atoll was used for nuclear testing, and the last such test was conducted in 1962.

Today, Johnston Atoll is a National Wildlife Refuge, managed by the United States Fish and Wildlife Service. It is home to a variety of marine and bird life, including the endangered green sea turtle, the threatened Hawaiian monk seal, and several species of seabirds. Access to the atoll is restricted, and only a small number of researchers and other authorized personnel are allowed to visit each year.