city vs Rockford

city and Rockford both are nouns.

Word	Noun	Adjective	Verb	Adverb
city	Yes	No	No	No
Rockford	Yes	No	No	No

city (noun)	Rockford (noun)
people living in a large densely populated municipality	a city in northern Illinois
a large and densely populated urban area; may include several independent administrative districts
an incorporated administrative district established by state charter