Citizenship Day also known as Constitution Day is a federal holiday in the USA, and observed on September 17, 2021. On that day in 1787 the adoption of the United States Constitution was signed by delegates to the Constitutional Convention in Philadelphia. This event commemorates also all the people who are taking steps to become U.S. citizens and those who become citizens by coming of age or by naturalization.
The origins of this celebration goes back to 1940 when the day was called "I am an American Day" and celebrated on the third Sunday in May each year. Later the day was renamed in Citizenship Day and moved to September 17 by the Congress.