On 15 May 1939, John J. Lynch of the U.S. Bureau of Biological Survey located 13 whooping cranes (Grus americana), including 2 prefledged young, during an aerial survey near White Lake in southwestern Louisiana. His observation was the last historic record of whooping cranes breeding in the wild in the United States, and it confirmed the presence of a nonmigratory breeding population along the Gulf Coast. While reviewing old U.S. Fish and Wildlife Service files at the National Archives in 1999, we located Lynch's original 1939 field note, 2 letters, 5 photographs, and a draft manuscript describing the discovery; 4 other related letters also were found. Because of their biological and historical interest, we have reproduced the documents in this paper. A thorough assessment of the White Lake marshes as a potential site for returning nonmigratory whooping cranes to southwestern Louisiana should be conducted.