Illinois is located in the Midwestern United States and has a continually expanding economy that has transformed the state from a once-sprawling wilderness to one of the most productive industrial and agricultural states in the union. A dense network of highways, railroads, air routes, and waterways converging on the city of Chicago make it one of the principal transportation centers in the United States. The Chicago metropolitan area accounts for two-thirds of the Illinois population. Chicago is also recognized as a commercial and industrial center, serving as host to the world’s first and largest derivatives exchange market (the Chicago Mercantile Exchange). The city is also a leading cultural center, featuring world-renowned museums and libraries. Illinois was mainly pioneer land until railroad construction in the 1850s spurred further economic development. Even with the strength of other industries, Illinois ranks in the top five most productive farming states in the nation.