Chicago is the third most populous city in the United States, located in Illinois. The city is known for its architecture, art, culture, and history. Chicago is also a significant hub for business, transportation, and tourism. If you want to travel to Chicago, find cheap flights from Denver to Chicago for $400. Fly from Denver on Frontier, Spirit Airlines, and more. Search for Chicago flights on First Fly Travel now for the best deal. You can call our customer care executive anytime at +1-866-383-9353.