Article III of the Constitution provides that “judicial power of the United States, shall be vested in one Supreme Court, and such inferior courts” as Congress sees fit to establish. Article III establishes neither how many justices should sit on the Supreme Court, nor the structure of federal courts. The Judiciary Act of 1789 filled this gap by providing that “the supreme court of the United States shall consist of a chief justice and five associate justices.” The Act also created federal District Courts and a Circuit Court, which would hear appeals from the district courts and would become the Courts of Appeals.
Under the Act, the District Courts had jurisdiction over serious federal crimes, civil cases over $500 involving diversity jurisdiction or the United States as a party, and admiralty cases. That is, the Judiciary Act of 1789 did not grant District Courts federal question jurisdiction, over which they currently have jurisdiction.
A transcript of the Judiciary Act of 1789 may be found here.
[Last updated in December of 2021 by the Wex Definitions Team]