NINE JUSTICES MAKE up the U.S. Supreme Court: one chief justice and eight associate justices. But it hasn’t always been this way. For the first 80 years of its existence, the Supreme Court fluctuated in size from as few as five to as many as 10 before settling at the current number in 1869. Here’s how the court ended up with nine justices—and how that could change.

Constitutional foundations

When the Founding Fathers set out to establish the U.S. Supreme Court at the Constitutional Convention in 1787, they kept the details vague. There are no constitutional requirements for age, experience, or citizenship of Supreme Court justices, nor did the Constitution establish how many justices would make up the court. Instead, it left many of the details up to Congress and the president. 

Two years later, the first Congress passed the Judiciary Act of 1789—signed into law by George Washington on September 24, 1789—which established a court of six justices responsible for ensuring the constitutionality of laws enacted by the executive and legislative branches.

The law placed the Supreme Court at the top of a three-tier federal court system. At the lowest level, each state would have a federal judge presiding over district courts hearing minor cases related to federal laws as well as maritime cases. Those districts were then organized into three geographical regions with circuit courts that would both serve as trial courts and hear appeals.

Rather than create judgeships for each circuit court, though, Congress stipulated that two Supreme Court justices and one local district court judge would sit on circuit court panels. Each of the six justices was assigned a geographical circuit and required to preside over their circuit courts twice a year, meaning they were on the road for much of the year.

Partisan squabbles

It didn’t take long for the make-up of the courts to become a partisan issue. In 1801, Federalist party members in Congress sought to expand federal jurisdiction over the states by reorganizing the court system. Congress passed the Judiciary Act of 1801, creating new judgeships to serve six judicial circuits and reducing the Supreme Court from six seats to five. In so doing, the law also eliminated the practice of “riding circuit,” the cross-country travel which the Supreme Court justices detested.

Federalist John Adams, the second president of the United States, signed the bill into law on February 13, 1801. But the signing came just after he had lost his reelection campaign to political rival Thomas Jefferson, and the move was seen as an attempt to limit his successor’s appointments to the court. Jefferson quickly repealed the bill when he took office before any changes to the court’s composition could take effect. Since Supreme Court seats are lifetime appointments, the law had not removed any justices from the court but simply stipulated that the next vacant seat would not be replaced.

With the repeal, the six Supreme Court justices resumed their circuit riding duties. This time, rather than assign the justices to circuits, Jeffersonian Republicans instructed the six Supreme Court justices to allot themselves to the circuits “as they shall think fit.”