Charles E. King wrote "Ke Kali Nei Au" ("Waiting here for you") in 1926 for his operetta, Prince of Hawaii. In 1958, Al Hoffman and Dick Manning wrote a 'singable English translation' of the Hawaiian words, and Andy Williams had a pop hit with it as the "Hawaiian Wedding Song" (which was later recorded by Elvis Presley and others).
I'm not sure King's original song would be called "folk," but Andy Williams's and Elvis's versions were clearly pop.