H.R. 334, An Act to fix the Number of Judges of the Supreme Court . . . and to change certain Judicial Circuits (Judicial Circuits Act of 1866), June 13, 1866
Throughout the nineteenth century, Congress made frequent changes to the federal judicial circuits. In 1866 Congress passed the first major judicial legislation after the Civil War: the Judicial Circuits Act of 1866. It reduced the circuits from ten to nine, redrew their boundaries, and authorized the gradual reduction of Supreme Court seats from ten to seven.
Records of the U.S. Senate, National Archives and Records Administration
Redrawing Federal Court Circuits
Congress originally assigned Supreme Court justices to serve on circuit courts, which tried cases and heard appeals from district courts. Congress also determined circuit boundaries, redrawing them periodically. Prior to the Civil War, the president appointed a justice from each circuit. Five of the nine circuits were completely comprised of slave-holding states. After the war, the Judiciary Circuits Act of 1866 redrew circuit boundaries to weaken the influence of Southerners on the Supreme Court.
Congress determines the structure and authority of the federal court system. After the Civil War, Congress significantly revised the federal circuit courts and the number of Supreme Court justices.