Southern United States vs Mississippi

Southern United States and Mississippi both are nouns.

Word	Noun	Adjective	Verb	Adverb
Southern United States	Yes	No	No	No
Mississippi	Yes	No	No	No

Southern United States (noun)	Mississippi (noun)
the region of the United States lying to the south of the Mason-Dixon line	a state in the Deep South on the gulf of Mexico; one of the Confederate States during the American Civil War
	a major North American river and the chief river of the United States; rises in northern Minnesota and flows southward into the Gulf of Mexico