(Oops, yes this is a day late.)
Sept. 17th is Constitution Day, celebrating the anniversary of the signing of the U.S. Constitution in 1787.
For more information:
Constitution Day resources from the National Constitution Center
Resources for students and Educators from the National Archives
Constitution Day research guide from LLRX
The Colorado Courts Celebrate Constitution Day (2006) - message from Chief Justice Mary Mullarkey, from the Colorado Courts website