Illinois (Illinois) is in the Midwest region of the United States, with a land area of 146,000 square kilometers and a population of more than 12 million. The capital of the state is Springfield (Springfield), which is also translated as "Springfield City". This is a landlocked state with relatively flat terrain, with plains and hills. The largest city in Illinois is Chicago, which is also the manufacturing center of the United States, where the steel industry and automobile industry are well developed. Because of the developed industry, Chicago's transportation is extremely convenient. There are more than 30 railways gathering here. Important airports are: Chicago O'Hare International Airport and Chicago Midway International Airport. The ZIP code for Illinois starts with IL and the area code is 217. The zip code of the capital city of Springfield starts from 62701, the zip code of Chicago (Chicago) starts from 60601, and the zip code of other cities Rockford (Rockford) starts from 61101.