Ward v. United States was a Supreme Court case decided in 1870. The case involved a dispute between the United States and the Ward family over a parcel of land in the state of California. The Ward family had purchased the land from the Mexican government in 1845, and had been living on the land since that time. The United States government, however, claimed that the land was part of the public domain and had been since 1848, when the Treaty of Guadalupe Hidalgo was signed. The Supreme Court ultimately sided with the Ward family, ruling that the land was not part of the public domain and that the Ward family had a valid claim to the land. The Court held that the Treaty of Guadalupe Hidalgo did not apply to the land in question, as it was not part of the territory ceded by Mexico to the United States. The Court also held that the Ward family had acquired a valid title to the land in 1845, and that the United States had not acquired any title to the land. As a result, the Ward family was allowed to keep the land.

In Ward v. United States, the Supreme Court was asked to decide whether a defendant could be convicted of manslaughter for killing another person while in the act of committing a felony. The majority opinion held that such an act constituted manslaughter and thus could be punished as such. However, Justice Field dissented from this decision on two grounds: firstly, he argued that there was no precedent for punishing someone who killed another person while in the commission of a felony; secondly, he argued that Congress had not intended to punish such acts when it passed laws criminalizing certain felonies. He concluded by stating his belief that if Congress wished to make killing during the commission of a felony punishable then they should have done so explicitly rather than relying upon judicial interpretation and inference.