List of United States Supreme Court cases, volume 121

This is a list of cases reported in volume 121 of United States Reports, decided by the Supreme Court of the United States in 1887.

Justices of the Supreme Court at the time of volume 121 U.S.
The Supreme Court is established by Article III, Section 1 of the Constitution of the United States, which says: "The judicial Power of the United States, shall be vested in one supreme Court . . .". The size of the Court is not specified; the Constitution leaves it to Congress to set the number of justices. Under the Judiciary Act of 1789 Congress originally fixed the number of justices at six (one chief justice and five associate justices). Since 1789 Congress has varied the size of the Court from six to seven, nine, ten, and back to nine justices (always including one chief justice).

When the cases in volume 121 U.S. were decided the Court comprised the following nine members:

Ex parte Bain
In Ex parte Bain, 121 U.S. 1 (1887), the Supreme Court held that when an indictment is filed with a federal court, no change can be made in the body of the instrument by order of the court or by the prosecuting attorney without resubmitting the case to the grand jury. Even though a court may deem a change immaterial, the instrument, as revised, is no longer the indictment of the grand jury which presented it. Bain was overruled in part by the Court in United States v. Cotton, 535 U.S. 625 (2002).

Citation style
Under the Judiciary Act of 1789 the federal court structure at the time comprised District Courts, which had general trial jurisdiction; Circuit Courts, which had mixed trial and appellate (from the US District Courts) jurisdiction; and the United States Supreme Court, which had appellate jurisdiction over the federal District and Circuit courts—and for certain issues over state courts. The Supreme Court also had limited original jurisdiction (i.e., in which cases could be filed directly with the Supreme Court without first having been heard by a lower federal or state court). There were one or more federal District Courts and/or Circuit Courts in each state, territory, or other geographical region.

Bluebook citation style is used for case names, citations, and jurisdictions.
 * "C.C.D." = United States Circuit Court for the District of . ..
 * e.g.,"C.C.D.N.J." = United States Circuit Court for the District of New Jersey
 * "D." = United States District Court for the District of . ..
 * e.g.,"D. Mass." = United States District Court for the District of Massachusetts
 * "E." = Eastern; "M." = Middle; "N." = Northern; "S." = Southern; "W." = Western
 * e.g.,"C.C.S.D.N.Y." = United States Circuit Court for the Southern District of New York
 * e.g.,"M.D. Ala." = United States District Court for the Middle District of Alabama
 * "Ct. Cl." = United States Court of Claims
 * The abbreviation of a state's name alone indicates the highest appellate court in that state's judiciary at the time.
 * e.g.,"Pa." = Supreme Court of Pennsylvania
 * e.g.,"Me." = Supreme Judicial Court of Maine