This is the 3810th most frequent Korean word.
시카고
Chicago (a city in the United States).
In this sentence, '시카고' is used as a proper noun to refer to the city Chicago.
시카고는 미국에서 세 번째로 큰 도시입니다.
Chicago is the third largest city in the United States.
Here, '시카고' is used as the object of the verb '방문하다' (to visit), indicating the location visited.
저는 작년에 시카고를 방문했어요.
I visited Chicago last year.
In this example, '시카고' is used possessively with '의' to describe a related attribute of the city, its landmark.