Constitution Day and Citizenship Day is observed every September 17th.
"Constitution Day and Citizenship Day commemorate the formation and signing on September 17, 1787, of the Constitution and recognize all who, by coming of age or by naturalization, have become citizens."
Our American Government. U.S. Congress, Joint Committee on Printing. House Document 108-94 (108th Congress, 1st Session). Washington, DC: U.S. Government Printing Office, 2003.
University of Delaware Library Annex U.S. Documents Y 1.1/7:108-94