Green’s Dictionary of Slang

(US) the militia.

1862		R.B. Hayes Diary and Letters (1922) II 192: Three thousand milish are [...] on or near Flat Top Mountain.
1883		Daily Kansas State Journal 7 June in Miller & Snell Why the West was Wild 559: Another call for the ‘milish’ is expected by tomorrow morning.
1907		D. Runyon ‘The Defence of Strikerville’ in From First To Last (1954) 11: The sad circumstances of J. Wallace Hanks’ enlistment in the Colorado State milish.