I don't have my earlier sources handy, but I found this at Wikipedia: Red River Valley

"Edith Fowke offers anecdotal evidence that the song was known in at least five Canadian provinces before 1896 ... [leading] to speculation that the song was composed at the time of the Wolseley Expedition to the northern Red River Valley of 1870 in Manitoba. ..."

and

"The earliest written manuscript of the lyrics, titled "Red River Valley", bears the notations 1879 and 1885 in locations Nemha and Harlan in western Iowa, so it probably dates to at least that era."