U.S. Constitution Day September 17 Sept. 17, 1787, is the official birthday of our government, the date on which delegates to the Philadelphia Convention completed and signed the U.S. Constitution. The ideas on which America was founded — commitments to the rule of law, limited government, and the ideals of liberty, equality, and justice — are embodied in the Constitution, the oldest written constitution of any nation. To learn more about the Constitution, visit constitutionfacts.com.