"Nobody said anything about druthers." Mark Twain in Huck Finn
"There ain't any druthers about it." Mark Twain in Tom Sawyer, 1876.
"I'd druther they was devils a dern sight." Mark Twain in Tom Sawyer, 1876.

Definition in Oxford English Dictionary (1987 Supplement and later complete edition): A choice, preference. Dialectical American alteration of I (you, etc.) would rather.
Drather(s) has also been noted.

The word may be much older, and could be sought for in letters and diaries and possibly newspapers. Before Mark Twain, there was little dialectical literature published in USA.