Thomson v. Dean was a United States Supreme Court case that was decided in 1868. The case involved a dispute between two parties over the ownership of a piece of land in the state of Missouri. The plaintiff, Thomson, claimed that he had purchased the land from the defendant, Dean, in 1854. Dean, however, argued that the sale was invalid because he had not been given proper notice of the sale. The Supreme Court ultimately sided with Thomson, ruling that Dean had been given sufficient notice of the sale and that the sale was valid. The Court held that the notice given to Dean was sufficient to put him on notice of the sale and that he had failed to take any action to contest the sale. The Court also held that the sale was valid under Missouri law, as the sale had been made in good faith and for a fair price. The decision in Thomson v. Dean established that notice of a sale must be given to all parties involved in order for the sale to be valid. It also established that a sale must be made in good faith and for a fair price in order to be valid under state law. This case has been cited in numerous subsequent cases involving the validity of sales and the notice requirements for such sales.

In Thomson v. Dean, the Supreme Court was asked to decide whether a state court had jurisdiction over a case involving citizens of different states. The majority opinion held that it did not have such jurisdiction and thus dismissed the appeal. However, Justice Field dissented from this decision on two grounds: firstly, he argued that Congress had given state courts concurrent jurisdiction in cases between citizens of different states; secondly, he contended that even if there were no explicit congressional grant of power to state courts in such cases, they should still be allowed to exercise their traditional common law powers as long as those powers do not conflict with federal laws or treaties. In conclusion, Justice Field believed that the lower court's ruling should stand because it was within its authority under both federal and common law principles.