This US Supreme Court case involved Isabella Mackey, widow of James Mackey, and her heirs John Zenon Mackey and others. The appellants argued that the United States had wrongfully taken possession of land belonging to them in Florida which was granted to their ancestor by a Spanish grant. They claimed that this constituted an infringement on their rights as citizens under the Constitution and sought damages for it. The Supreme Court held that although they were entitled to compensation for any losses suffered due to the taking of their property, they could not recover damages from the United States because it was acting within its sovereign powers when it took possession of the land in question. Furthermore, since there was no evidence presented showing bad faith or fraud on behalf of either party during negotiations over ownership rights prior to litigation being initiated, no further relief could be provided by way of monetary compensation or otherwise.

In Isabella Mackey Widow, John Zenon Mackey and Others, Heirs of James Mackey v. The United States, the Supreme Court was asked to decide whether a certain tract of land in Louisiana belonged to the heirs of James Mackey or to the United States. In an opinion delivered by Justice Story for a majority of five justices, it was held that title had passed from Mr.Mackey's estate to the government under two separate grants made by Congress in 1811 and 1820 respectively; thus affirming a decision rendered by Circuit Court for Louisiana. However Chief Justice Marshall dissented on behalf of himself and three other Justices arguing that although there were some ambiguities with respect to one grant (1811), he believed that both grants should be interpreted together as they related back to each other; therefore concluding that title had not been transferred from Mr.Mackeys' estate but remained vested in his heirs at law instead.