Chicago is 1,382 times larger than Vatican.
Area: 0 km2 World Factbook
Population: 842 (July 2014) World Factbook
Vatican City, officially Vatican City State, is one of the last six remaining absolute monarchies whose territory consists of a walled enclave within the city of Rome. It has an area of approximately 44 hectares, and a population of around 840. Wikipedia
Area: 608 km2 calculated
Chicago is the third most populous city in the United States, after New York City and Los Angeles. With 2.7 million residents, it is the most populous city in both the U.S. state of Illinois and the American Midwest. Wikipedia