It is a country song and there are several sets of words.
One versions is:
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I will sing you one O
Green grow the rushes O
What is your one O
One is one and all alone
And evermore shall be so
I will sing you two O
Green grow the rushes O
What is your two O
Two, two the lily white boys
Clothed all in green O
I will sing you three O
Green grow the rushes O
What is your three O
Three, three the rivals
Four for the Gospel makers
Five for the symbols at your door
Six for the six proud walkers
Seven for the seven stars in the sky
Eight for the April rainers
Nine for the nine bright shiners
Ten for the Ten Commandments
Eleven for the eleven that went to heaven
Twelve for the twelve apostles