Blacklock v. Small was a United States Supreme Court case that dealt with the issue of whether a state court had the authority to issue a writ of habeas corpus to a prisoner who was being held in a federal prison. The case arose when a prisoner, Blacklock, was held in a federal prison in the state of Georgia. Blacklock sought a writ of habeas corpus from the state court, claiming that he was being held in violation of the Constitution. The state court granted the writ, and the federal government appealed the decision to the Supreme Court. The Supreme Court held that the state court did not have the authority to issue a writ of habeas corpus to a prisoner held in a federal prison. The Court reasoned that the writ of habeas corpus was a federal remedy, and that the state court did not have the power to interfere with the federal government's authority to imprison individuals. The Court also noted that the writ of habeas corpus was a remedy that could only be used to challenge the legality of a person's detention, and not to challenge the conditions of the detention. In conclusion, the Supreme Court held that the state court did not have the authority to issue a writ of habeas corpus to a prisoner held in a federal prison. The Court reasoned that the writ of habeas corpus was a federal remedy, and that the state court did not have the power to interfere with the federal government's authority to imprison individuals.

In Blacklock v. Small, the Supreme Court was tasked with determining whether a state court had jurisdiction to hear an appeal from a probate court's decision regarding the distribution of property in intestacy proceedings. The majority opinion held that it did not have such authority, as appeals from probate courts were only allowed when expressly provided for by statute or rule of practice. Justice Field dissented on this point and argued that while there may be no express statutory provision allowing for appeals in these cases, they should still be permitted under general principles of equity and justice. He further noted that if states are prevented from hearing such appeals then individuals would be deprived of their right to due process since they would not have any means to challenge decisions made by probate courts which could potentially affect their rights and interests significantly. As such, he concluded that state courts should indeed possess jurisdiction over these matters so as to ensure fairness and protect citizens' legal rights.