Answer: Citizenship Day and I Am an American Day
On September 17, 1787, the Constitutional Convention approved the United States Constitution in Philadelphia. One hundred and sixty-five years later, in 1952, the U. S. Congress designated the same day as Citizenship Day, a day to celebrate new U. S. citizens. Citizenship Day began as I Am An American Day, which Congress established in 1940, and which was to be held the third Sunday of every May. In 1946, President Harry S. Truman officially declared I Am An American Day on May 19th, saying, in part:
…I urge Federal, State, and local officials and patriotic, civic, and educational organizations to plan and hold, on or about May 19, exercise designated to help our new citizens, both native-born and naturalized, to understand more fully the significance and responsibilities of citizenship in our self-governing Republic, so that they may be better prepared to add strength to the common purpose of all our citizens that this Republic shall continue to maintain its place of leadership and service among the nations of the world.
In 1952, I Am An American Day was officially renamed Citizenship Day. And in 2004, the date of Citizenship Day was moved to September 17th to coincide with Constitution Day.
More images pertaining to I Am An American Day are available in the Philadelphia Record photograph morgue collection (#V07). In addition, HSP's library holds a number of titles on citizenship and on the history of the United States Constitution.