U.S. vs in

U.S. and in both are nouns.

Word	Noun	Adjective	Verb	Adverb
U.S.	Yes	No	No	No
in	Yes	Yes	No	Yes

U.S. (noun)	in (noun)
the executive and legislative and judicial branches of the federal government of the United States	a unit of length equal to one twelfth of a foot
North American republic containing 50 states - 48 conterminous states in North America plus Alaska in northwest North America and the Hawaiian Islands in the Pacific Ocean; achieved independence in 1776

U.S. (adverb)	in (adverb)
	to or toward the inside of