Kauai or Kauai is the oldest of the main Hawaiian Islands. With an area of 552.3 square miles (1,430.5 km2), it is the fourth largest of the main islands in the Hawaiian archipelago and the 21st largest island in the United States. Known also as the Garden Isle, Kauai lies 105 miles (170 kilometers) across the Kauai Channel, northwest of Oahu. The United States Census Bureau defines Kauai as Census Tracts 401 through 409 of Kauai County, Hawaii, which is all of the county except for the islands of Kaula, Lehua, and Niihau. The 2000 census population of Kauai (the island) was 58,303. During the reign of King Kamehameha, the islands of Kauai and Niihau were the last Hawaiian Islands to join his Kingdom of Hawaii. Their ruler, Kaumualii, resisted Kamehameha for years. King Kamehameha twice prepared a huge armada of ships and canoes to take the islands by force and twice failed; once due to a storm, and once due to an epidemic. In the face of the threat of a further invasion, however, Kaumualii decided to join the kingdom without bloodshed, and became Kamehameha’s vassal in 1810, ceding the island to the Kingdom of Hawaii upon his death.