Iceland regained its independence on December 1, 1918, but still remained in a personal union with Denmark. From that time on, December 1 was celebrated as the National Day, which in 1944 was moved to June 17.
The change of date came as a result of the official announcement on June 17, 1944, during the meeting at Lake Þingvellir, of the founding of the Republic of Iceland. Since then, this day has been a national holiday.
For good reason June 17 was declared Independence Day. It is also the date of birth Jón Sigurðsson (1811–1879), leader of the 19th-century independence movement in Iceland.
After studying in Denmark, he served as an MP in Iceland and led his countrymen to free themselves from Denmark. Five years before his death, in 1879, Iceland established a new constitution which gave it autonomy in internal affairs.
According to tradition, Independence Day is opened by a woman dressed in traditional clothes “Women of the Mountains”- Fjallkonan. Fjallkonan has become a symbol of Iceland’s struggle for independence.
Source: Yle