Sheet music for WHIP-POOR-WILL'S SONG, composed by H. Millard, can be seen in The Good Old Songs We Used to Sing, Volume 2 compiled by J. C. H. (Boston: Oliver Ditson Company, 1895), page 115.

Lyrics are the same as those posted by Melissa above, so I won't repeat them.

It has the notation: "The echo of the Whip-poor-will may be repeated by another voice at a distance, or in another room, with very fine effect."!