Replica parchment U.S. Constitution. Looks great in a display case. Measures: 11.75" x 17" The United States Constitution is the supreme law of the United States of America. It was adopted in its original form on September 17, 1787 by the Constitutional Convention in Philadelphia, Pennsylvania, and later ratified by the people in conventions in each state in the name of "We the People." The Constitution has a central place in American law and political culture. It is the oldest written national constitution of its type still in effect in the world.