John Macgwire v. Mary L. Tyler et al was a case heard by the United States Supreme Court in 1868. The case involved a dispute between Macgwire and Tyler over the ownership of a piece of land in the state of Missouri. Macgwire had purchased the land from the United States government in 1854, but Tyler claimed that she had purchased the land from the same government in 1856. The Supreme Court ruled in favor of Macgwire, finding that he had acquired the land first and that Tyler's claim was invalid. The Court held that the United States government had no authority to sell the same piece of land twice, and that Macgwire's purchase was valid. The Court also held that Tyler's claim was barred by the statute of limitations, as she had waited too long to bring her claim. The decision in this case established the principle that the United States government cannot sell the same piece of land twice, and that a claim to land must be brought within a certain period of time in order to be valid. This case is still cited today in cases involving disputes over land ownership.

John Macgwire brought a case against Mary L. Tyler and others in the Supreme Court of the United States, claiming that he was entitled to an undivided one-third interest in certain real estate located in Washington County, Maryland. The majority opinion held that Macgwire had no right to such an interest because his deed did not specify any fractional share of the property; instead it simply conveyed "all my right title and interest" without specifying what portion thereof belonged to him. However, Justice Field dissented from this decision on the grounds that when a deed conveys all rights without specifying any particular amount or proportionate part thereof, then it should be construed as conveying whatever legal interests were vested with its grantor at the time of conveyance. In other words, since Macgwire's deed indicated that he owned some kind of legal interest prior to its execution (as evidenced by his ability to transfer said rights), then he must have been granted some form of ownership over those same interests upon executing his deed - even if there was no explicit mention made therein regarding how much or what type of ownership he received. Thus according Field's dissent, John Macgwire should have been awarded an undivided one-third interest in accordance with his original claim.