(The singer meets a young cowboy "all dressed in white linen and cold as the clay.") The cowboy has been shot (or given a venereal disease?) and is dying. He regrets his carousing, gives instructions for his burial, and dies.
One of the large group of ballads ("The Bard of Armagh," "Saint James Hospital," "The Streets of Laredo") ultimately derived from "The Unfortunate Rake." All use the same tune and metre, and all involve a person dying as a result of a wild life, but the nature of the tragedy varies according to local circumstances.
Thorp/Fife studied 150 versions of this text, and determined that 39 were set in "The Streets of Laredo" or similar; 37 took place at Tom Sherman's Barroom or similar, 25 used other words starting with LA (Lafferty, London, Laden, etc.), 31 (not all of them variants of this exact song) used miscellaneous places, and 18 were not localized.
Logsdon, pp. 289-290, reports that "Tom Sherman's barroom was a popular cowboy dance hall and bar in Dodge City, Kansas." He cites a claim that this song was written by Francis Henry Maynard in 1876, and claims that Tom Sherman's was the location in this original text. Based on the dates at which the song was collected, this is possible, but I haven't listed Maynard as the author because the evidence is so thin. Logsdon quoted an article in which Maynard allegedly described the circumstances of the composition.
For the treatment of syphilis prior to the twentieth century, see the notes to "The Unfortunate Rake." - RBW