Here's my two cents...
Just back from a family history trip to Sioux City, Iowa, where I was informed that back in the late-1800's, my great-great-grandfather John McDonald, who owned a large farm, and also served as sheriff of Sioux City for a span of several years (1871-1879), hosted a man from New York on his farm for several days. After the visitor returned to New York, he supposedly wrote a song about "the farm" he had visited, and that's where the present-day version originated...IF you believe in oral family history. Add to that, my 11 year old son's belief ;-) that the chorus "Ee-I-Ee-I-O" was at some time in the past cut short from the original "Ee-I-Ee-I-Owa", thus connecting the song with its Iowa roots. Of course, I've seen others on the internet claiming similar connections to the song, but this one's new to me so I thought I'd throw it out there for others to comment on...