Johnston Atoll is a 1.03 sq mi (2.7 km²) atoll in the North Pacific Ocean about 750 nmi (860 mi; 1,390 km) west of Hawaii. The atoll, which is located on the coral reef platform, comprises four islands. Johnston and Sand islands are both enlarged natural features, while North (Akau) and East (Hikina) are two artificial islands formed by coral dredging. Johnston Atoll is grouped as one of the United States Minor Outlying Islands.

For nearly 70 years, the atoll was under the control of the American military. In that time it was used as an airbase, a naval refuelling depot and a weapons testing area. In the mid 1980s, the atoll became a facility for Chemical weapons disposal. In 2004 the military base was closed; island control was handed over to civilian authorities.

Johnston is an unincorporated territory of the United States administered by the United States Fish and Wildlife Service of the Department of the Interior as part of the Pacific Remote Islands Marine National Monument.

The first European record of the atoll was on September 2, 1796 when the American brig Sally accidentally grounded on a shoal near the islands. The ship's captain, Joseph Pierpont, published his experience in several American newspaper the following year giving an accurate position of Johnston and Sand Island along with part of the reef. However he did not name or lay claim to the area. The islands were not officially named until Captain Charles J. Johnston of the Royal Naval ship HMS Cornwallis sighted them on December 14, 1807.