See also: Map of Federal Judicial Circuits

Since the inauguration of the federal government, judicial circuits have provided geographical and administrative structure for the federal court system. For more than a century, the circuits functioned primarily as a way of assigning the justices and, after 1869, the circuit judges to service on the trial courts. The circuits and their courts embodied the federal character of the judicial system, connecting trial courts in districts that conformed to state borders and were governed by local legal procedures with a Supreme Court that had final jurisdiction over all of the nation's courts.

The Judiciary Act of 1789 arranged the judicial districts of the eleven existing states into three circuits, the Eastern, the Middle, and the Southern, and provided that justices of the Supreme Court would serve on the U.S. circuit courts that convened in the districts within a particular circuit. Congress regularly expanded and reorganized the system of judicial circuits during the first 70 years of the federal government. The number of circuits increased to six in 1801, seven in 1807, nine in 1837, and ten in 1855. Congress made even more frequent changes in the arrangement of states within the circuits in order to incorporate new states and to accommodate the demanding travel schedules of the Supreme Court justices. Occasionally entire states or districts within a state were omitted from the circuits because justices could not regularly attend courts far from established transportation routes. Only in 1889 was every district included within a circuit. With one exception in the mid-nineteenth century, the circuits have consisted of adjoining states.

In 1866 Congress reorganized the states into nine circuits and established the geographical outline that has remained unchanged except for the inclusion of new states within existing circuits and the division of two circuits. In 1929, Congress divided the Eighth Circuit to create a Tenth Circuit, and in 1980 an Eleventh Circuit was established to include three states formerly part of the Fifth Circuit. The act establishing the circuit courts of appeals in 1891 gave the circuits a new jurisdictional role at the same time that reliance on the existing circuit organization gave the judiciary's principal appellate courts a regional identity. (The Federal Circuit, established in 1982, is the only circuit defined exclusively by its jurisdiction.) In the twentieth century, the circuits have become increasingly important for the administrative organization of the federal courts. Representation on the Judicial Conference and its predecessor, the Conference of Senior Circuit Judges, has been allocated by circuit. The circuit judicial councils established in 1939 exercise administrative authority over all the federal courts within a circuit, and the circuit judicial conferences provide a forum for judges and lawyers to discuss the administration of federal justice within a circuit.