How to sing Red River Valley in your key
Red River Valley spans 12 semitones (D4 to D5 in its usual key), 38 notes. That's an octave or less, so it fits most voices once it's in the right key.
Words
From this valley they say you are going,
We will miss your bright eyes and sweet smile,
For they say you are taking the sunshine
That has brightened our pathway a while.
Finding your key
A song is in your key when its highest note sits at or just below the top of your comfortable range. Measure your range, then move the melody so its top note (D5 here) lands one or two semitones under your easy top. Singsteady does this for you and scores every note as you sing.
traditional, by 1879. Melody and words are in the public domain. Notes transcribed from the score in Wikipedia, “Red River Valley (song)” (score).