Chicago is a city.
Chicago ( [ ʃᵻˈkɑːɡoʊ ] or [ ʃᵻˈkɔːɡoʊ ] ) , officially the City of Chicago , is the third-most populous city in the United States . With over 2.7 million residents , it is also the most populous city in both the state of Illinois and the Midwestern United States . In 2012 , Chicago was listed as an alpha global city by the Globalization and World Cities Research Network , and ranked seventh in the world in the 2016 Global Cities Index . A county seat is an administrative center , seat of government , or capital city of a county or civil parish .