United States v. Le Baron was a United States Supreme Court case that dealt with the issue of whether a federal court had jurisdiction over a case involving a contract dispute between two private parties. The case arose when the defendant, Le Baron, entered into a contract with the plaintiff, the United States, to build a lighthouse in the state of Maine. Le Baron failed to complete the project and the United States sued him for breach of contract. The Supreme Court held that the federal court had jurisdiction over the case because the contract was made under the authority of the United States. The Court reasoned that the contract was made in the exercise of the federal government's power to regulate commerce and navigation, and thus was within the scope of the federal court's jurisdiction. The Court also held that the contract was valid and enforceable, and that the United States was entitled to damages for the breach of contract. The decision in United States v. Le Baron established the principle that federal courts have jurisdiction over contract disputes between private parties that are made under the authority of the United States. This principle has been applied in numerous cases since then, and is an important part of the federal court system.

In United States v. Le Baron, the Supreme Court was tasked with determining whether a tax imposed on distilled spirits by Congress in 1862 was constitutional. The majority opinion held that it was, finding that Congress had the power to impose taxes for revenue purposes under its authority to lay and collect taxes granted by Article I of the Constitution. However, Justice Field dissented from this ruling, arguing that while Congress may have been able to levy an excise tax on distilled spirits as part of its taxing powers under Article I of the Constitution, it could not do so without first apportioning such a tax among states according to their population size as required by Article I Section 9 Clause 4. He argued further that since no such apportionment had occurred prior to imposing this particular excise tax on distilled spirits in 1862, then it must be unconstitutional and thus invalidated.