From WIKIPEDIA

"I Wonder as I Wander" has its origins in a song fragment collected on July 16, 1933 by folklorist and singer John Jacob Niles.^{[1][2][3][4][5]} While in the town of Murphy in Appalachian North Carolina, Niles attended a fundraising meeting held by evangelicals who had been ordered out of town by the police.^[1][5] In his unpublished autobiography, he wrote of hearing the song:

A girl had stepped out to the edge of the little platform attached to the automobile. She began to sing. Her clothes were unbelievable dirty and ragged, and she, too, was unwashed. Her ash-blond hair hung down in long skeins.... But, best of all, she was beautiful, and in her untutored way, she could sing. She smiled as she sang, smiled rather sadly, and sang only a single line of a song.^[2]

The girl, named Annie Morgan, repeated the fragment seven times in exchange for a quarter per performance, and Niles left with "three lines of verse, a garbled fragment of melodic material—and a magnificent idea".^[5][2] (In various accounts of this story, Niles hears between one and three lines of the song.^[2][5][4][6]) Based on this fragment, Niles composed the version of "I Wonder as I Wander" that is known today, extending the melody to four lines and the lyrics to three stanzas