Ex parte De Groot is a United States Supreme Court case that dealt with the issue of property rights. The case involved a dispute between two parties over the ownership of a piece of land in New York. The plaintiff, De Groot, claimed that he had purchased the land from the original owner, while the defendant, Van Wagenen, argued that he had inherited the land from his father. The Supreme Court ruled in favor of De Groot, finding that he had acquired the land through a valid purchase. The Court held that the defendant had no right to the land, as he had not proven that he had inherited it from his father. The Court also held that the defendant had no right to the land under the doctrine of adverse possession, as he had not been in possession of the land for the required period of time. The Court's decision in Ex parte De Groot established the principle that a valid purchase of land is superior to any claim of inheritance or adverse possession. This ruling has been cited in numerous subsequent cases involving property rights.

In Ex Parte De Groot, the Supreme Court of the United States was asked to decide whether a New York court had properly granted guardianship over an elderly woman's estate. The majority opinion held that the state court did not have jurisdiction in this case and overturned its decision. However, Justice Field dissented from this ruling and argued that it should be left up to each individual state to determine how best to handle such matters within their own borders. He believed that since there were no federal laws governing guardianships at the time, states should be allowed autonomy in deciding how they wished to proceed with these cases. Furthermore, he argued that overturning a local court’s decision would set a dangerous precedent for future cases involving similar issues as well as undermine public confidence in state courts' ability to make sound decisions on behalf of citizens living within their jurisdictions.