Kohlsaat v. Murphy was a United States Supreme Court case that dealt with the issue of whether a state court could issue a writ of habeas corpus to a prisoner who was being held in a federal prison. The case arose when a prisoner, Murphy, was held in a federal prison in Illinois. Murphy sought a writ of habeas corpus from the state court, claiming that he was being held in violation of his constitutional rights. 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. The Court's decision in Kohlsaat v. Murphy established that state courts do not have the authority to issue writs of habeas corpus to prisoners held in federal prisons. The decision also clarified the scope of the writ of habeas corpus, and established that it could only be used to challenge the legality of a person's detention, and not to challenge the conditions of the detention.

Justice Field delivered the dissenting opinion in Kohlsaat v. Murphy, arguing that the majority's decision was incorrect and should be reversed. He argued that under Illinois law, a judgment creditor could not garnish wages from an employer without first obtaining a court order to do so. The majority had held that this requirement did not apply when the debtor was employed by someone who also happened to be his judgment creditor; however, Justice Field disagreed with this interpretation of Illinois law and found it contrary to both its letter and spirit. He further noted that such an interpretation would lead to absurd results since it would allow employers-judgment creditors to take advantage of their employees' wages without any judicial oversight or protection for those employees. In conclusion, he urged reversal of the lower court's ruling on these grounds as well as others raised by counsel for petitioner Kohlsaat which were omitted from consideration by the Court due to lack of time available at oral argument before rendering its decision.