Green’s Dictionary of Slang

Josh n.

[joskin n.]

(US) a rustic, a simpleton.

[US]W.W. Heartsill diary Fourteen Hundred and Ninety One Days in the Confederate Army (1992) 1 Aug. 141: We were ‘gobbled up’ and taken to the Arkansas Battalion H’d Q’rs [...] Luther says that the only thing he regrets in the affair is to be arrested by ‘Joshes’.
[[US] ‘South-Western Sl.’ in Overland Monthly (CA) Aug. 129: The cant designation in the Rebel army for a man of Arkansas was ‘Josh.’ This is said to have originated in a jocular attempt to compare Arkansas, Texas, and part of Louisiana to the two tribes and a half who had their possessions beyond Jordan, but went over with Joshua to assist the remaining tribes].
[US]N.Y. Times 25 July 10/5: The Chinaman calls all his gods by the generic name of Joss. The Californian, corrupting this into ‘Josh,’ asks, indignantly, ‘do you take me for a Josh?’ That is to say, an insensate idol, a block.
[US]‘Number 1500’ Life In Sing Sing 249: Josh. A country man.
[US]Monteleone Criminal Sl. (rev. edn).