United States v. Peck was a United States Supreme Court case that addressed the issue of whether the United States government had the authority to take possession of land that had been granted to a private individual by the state of Georgia. The case arose when the United States government sought to take possession of land that had been granted to a man named Peck by the state of Georgia. The government argued that the land was necessary for the construction of a military road. The Supreme Court held that the United States government did not have the authority to take possession of the land without first obtaining the consent of the state of Georgia. The Court reasoned that the United States government was not a party to the original grant of the land and, therefore, did not have the authority to take possession of it without the consent of the state. The Court also noted that the United States government had not provided any compensation to Peck for the land. The Court's decision in United States v. Peck established the principle that the United States government cannot take possession of land granted to a private individual by a state without first obtaining the consent of the state. This principle has been applied in numerous cases since then and remains an important part of the law today.

In United States v. Peck, the Supreme Court was tasked with determining whether a contract between two parties could be enforced when it had been made in violation of an existing law. The majority opinion held that the contract should not be enforced because it violated public policy and would encourage others to violate laws as well. Justice Field dissented from this decision, arguing that contracts are meant to protect private rights and interests, and thus should not be invalidated simply because they were made in violation of a law. He argued that if such contracts were voided every time there was a breach of law then no one would ever enter into any agreement for fear their rights might later be denied them on account of some technicality or other legal infraction having occurred during its formation or execution.