September 24, 1789 : First Supreme Court
The idea of a Supreme Court had first been outlined in Article 3 of the U.S. Constitution. Given final jurisdiction over all laws—especially those in which constitutionality was at issue—it was designed to be an integral part of a revolutionary system of checks and balances that would restrict any one area of government from becoming too powerful.
The first tribunal was made up of six justices: Chief Justice John Jay, and Associate Justices John Rutledge, William Cushing, John Blair, Robert Harrison, and James Wilson, all nominated by President Washington. Their first session took place on February 1, 1790, in New York City's Royal Exchange Building.
Over the next century, the number of justices would vary slightly before settling in just after the Civil War at the present number of nine.