It is celebrated annually on the third Friday in August to commemorate the anniversary of the state's 1959 admission to the Union.
[1] Statehood bills for Hawaii were introduced into the U.S. Congress as early as 1919 by Prince Jonah Kuhio Kalanianaole, the non-voting delegate sent by the Territory of Hawaii to the U.S. Congress.
In 1959, the U.S. Congress approved the statehood bill, the Hawaii Admission Act.
This was followed by a referendum in which Hawaiian residents voted 94% in support of statehood (the ballot question was: "Shall Hawaii immediately be admitted into the Union as a state?
"), and on August 21, 1959 (the third Friday in August), President Dwight D. Eisenhower signed a proclamation making Hawaii the 50th state.