The type specimen of a large, flightless marine bird, Hesperornis regalis, was collected by O.C. Marsh in 1871. Due to the practices of the time, and the lack of accurate maps, the type locality was initially recorded by Marsh in a letter simply as the “upper Cretaceous of Western Kansas,” and then later reported as “the gray shale near the Smoky Hill River in Western Kansas.” Since the Smoky Hill Chalk Member of the Niobrara Formation is exposed along the Smoky Hill River in present day Wallace, Logan and Gove counties over a distance of more than 75 miles, this vague locality information encompasses about 5 million years of depositional history. An 1880 account by Marsh narrows the locality down to the south bank of the Smoky Hill River about 20 miles east of Fort Wallace in Logan County. The results of a recent field investigation of the eastward route traveled by Marsh's 1871 Yale College Scientific Expedition sheds light on the probable locality of both the type specimen (YPM 1200) of Hesperornis regalis, and also the first specimen with a skull and teeth (YPM 1206) collected in 1872. In turn, this provides important new data supporting an earlier occurrence (Upper Santonian) of this species in the Western Interior Sea over Kansas than previously assumed.