McPherson v. Cox 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 mandamus to a county court. The case arose when the plaintiff, McPherson, sought to have the county court issue a writ of mandamus to the defendant, Cox, who was the county clerk. McPherson argued that the county court had the authority to issue the writ, while Cox argued that the state court had exclusive jurisdiction over the matter. The Supreme Court ultimately sided with McPherson, ruling that the county court had the authority to issue the writ of mandamus. The Court reasoned that the state court had no jurisdiction over the matter, as the writ of mandamus was a matter of local law. The Court further noted that the writ of mandamus was a common law remedy, and that the state court had no authority to interfere with the county court's decision. In conclusion, the Supreme Court ruled that the county court had the authority to issue the writ of mandamus, and that the state court had no jurisdiction over the matter. The Court's decision established that the county court had the authority to issue writs of mandamus in matters of local law.

Justice Field delivered the dissenting opinion in McPherson v. Cox, arguing that the majority's decision was contrary to established precedent and would lead to a dangerous expansion of federal power. He argued that Congress had no authority under Article IV, Section 3 of the Constitution to pass legislation granting exclusive jurisdiction over public lands within a state to any other party than the state itself. Furthermore, he noted that such an interpretation would be inconsistent with prior Supreme Court decisions which held that states have absolute control over their own property unless otherwise specified by Congress or prohibited by some other constitutional provision. Finally, Justice Field warned against allowing Congress too much leeway in determining what is "necessary and proper" for carrying out its powers as this could result in an undue extension of federal authority at the expense of individual states' rights.