Green’s Dictionary of Slang

(US) pertaining to the countryside or country culture.

1985		(con. 1969–70) D. Bodey F.N.G. (1988) 4: Everyone who has a hat on has a Boonie hat. Camouflaged jobs, like duck hunters wear.
1987		(con. 1968) Bunch & Cole Reckoning for Kings (1989) 302: The steel pots were abandoned for floppy boonie hats.
1987		‘Joe Bob Briggs’ Joe Bob Goes to the Drive-In 215: He’s sending Harry to a little boonie town called San Paulo.
1990		(con. c.1970) G. Hasford Phantom Blooper 170: A cheerful medic in a skuzzy boonie hat kneels down and whips out a morphine Syrette.
2003		N. Green Angel of Montague Street (2004) 48: He wore aviator glasses [...] topped with a boonie hat.
2008		T. Piccirilli Fever Kill 45: Nobody wanted to circuit boonie turf.