back country vs hinterland

back country and hinterland both are nouns.

Word	Noun	Adjective	Verb	Adverb
back country	Yes	No	No	No
hinterland	Yes	No	No	No

As nouns, back country and hinterland are synonyms defined as:

Other synonyms of back country include backwoods, boondocks.

back country (noun)	hinterland (noun)
a remote and undeveloped area	a remote and undeveloped area