United States v. Kelly is a United States Supreme Court case that was decided in 1872. The case involved a dispute between the United States and the defendant, Kelly, over the ownership of a parcel of land in the state of California. The United States argued that the land was part of the public domain and that Kelly had no right to it. Kelly argued that he had acquired the land through a valid grant from the Mexican government prior to the Mexican-American War. The Supreme Court held that the United States had a valid claim to the land, as it had been acquired through the Treaty of Guadalupe Hidalgo, which ended the Mexican-American War. The Court also held that Kelly had no valid claim to the land, as the Mexican government had no authority to grant it. The Court concluded that the United States was the rightful owner of the land and that Kelly had no right to it.

In United States v. Kelly, the Supreme Court was tasked with determining whether a tax imposed by Congress on distilled spirits was constitutional. The majority opinion held that it was not unconstitutional because the power to impose taxes is granted to Congress under Article I of the Constitution and this particular tax did not violate any other part of the Constitution. Justice Field dissented from this opinion, arguing that while Congress does have broad powers when it comes to taxation, there are limits as well; in his view, this particular tax exceeded those limits and thus violated both Article I and Amendment IX of the Constitution. He argued further that if such an expansive interpretation were allowed then all sorts of oppressive taxes could be imposed without regard for individual rights or state sovereignty - something he felt would be detrimental to our nation's system of government.