Hawaii is the most recent of the 50 U.S. states (joined the Union on August 21, 1959), and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean.
The state encompasses nearly the entire volcanic Hawaiian Island chain, which comprises hundreds of islands spread over 1,500 miles (2,400 kilometers). At the southeastern end of the archipelago, the eight "main islands" are (from the northwest to southeast) Niʻihau, Kauaʻi, Oʻahu, Molokaʻi, Lānaʻi, Kahoʻolawe, Maui, and the island of Hawaiʻi. The last is by far the largest and is often called "The Big Island" to avoid confusion with the state as a whole. The archipelago is physiographically and ethnologically part of the Polynesian subregion of Oceania.
Hawaii is the 8th-least extensive, the 11th-least populous, but the 13th-most densely populated of 50 U.S. states. Hawaii's coastline is approximately 750 miles (1,210 kilometers) long, which is fourth in the United States after Alaska, Florida, and California.