In the United States v. Constance Leblanc, Modest Leblanc, Louis Leblanc, Aspasia Leblanc, Joseph Leon and Raphael Broissard (the legal representatives and heirs at law of Pierre LeBlanc), the Supreme Court was asked to decide whether a certain tract of land in Louisiana belonged to the United States or to Pierre’s heirs. The case arose when Pierre died without leaving a will and his property passed by descent under Louisiana law. The government argued that it had acquired title through an 1803 treaty with France while the defendants claimed they were entitled as descendants of Pierre. After considering both sides' arguments, including evidence from surveys conducted before and after the treaty was signed, as well as other historical documents related to ownership claims over time for this particular piece of land; ultimately concluded that title did not pass from France to America but rather remained vested in Pierre's heirs at his death according to Louisiana laws governing succession rights upon death without a will.

In the case of United States v. LeBlanc, the Supreme Court was asked to decide whether a certain piece of land in Louisiana belonged to Pierre LeBlanc or to the United States. The majority opinion held that it belonged to the United States because they had acquired title from Spain before France ceded Louisiana and therefore their claim took precedence over any subsequent claims by private individuals like Pierre LeBlanc. However, Justice McLean dissented on this point and argued that while it is true that Spain had previously granted title for this land, there were no records showing how much money was paid for it or what conditions were attached; thus he concluded that since there was no evidence of payment being made by either party, neither could be said definitively to have superior rights over the other. He further noted that even if Spain did possess some kind of legal right at one time due to prior ownership, such rights would have been extinguished when France ceded Louisiana as part of its treaty with America in 1803. Therefore he reasoned that since both parties had equal standing under these circumstances then Pierre Leblanc should be allowed his rightful claim on this property without interference from either side