Stringfellow v. Cain was a United States Supreme Court case that addressed the issue of whether a state court could constitutionally impose a sentence of death for a crime that was not punishable by death at the time of its commission. The case involved a man named William Stringfellow, who was convicted of murder in the state of Louisiana in 1876. The state court sentenced him to death, despite the fact that the crime of murder was not punishable by death at the time of its commission. Stringfellow appealed his sentence to the Supreme Court, arguing that the state court had violated the Ex Post Facto Clause of the United States Constitution, which prohibits the retroactive application of laws. The Supreme Court agreed with Stringfellow, ruling that the state court had violated the Ex Post Facto Clause by imposing a sentence of death for a crime that was not punishable by death at the time of its commission. The Court held that the Ex Post Facto Clause was intended to protect individuals from the arbitrary and oppressive application of laws, and that the state court had violated this principle by imposing a sentence of death for a crime that was not punishable by death at the time of its commission.

In Stringfellow v. Cain, the Supreme Court was asked to decide whether a state court had jurisdiction over an action brought by a non-resident of the state against another non-resident who had been served with process outside of the state. The majority opinion held that such service was invalid and thus did not give rise to personal jurisdiction in the case. Justice Field dissented from this decision, arguing that due process requires notice before any judgment can be entered against someone and that it is reasonable for states to exercise their power over persons within their borders even if they are not residents. He argued further that since both parties were out of state at the time of service, there would have been no prejudice or harm done by allowing it in this instance as neither party could have been prejudiced by being subject to suit in a different forum than where they resided.