High Quality Content by WIKIPEDIA articles! Northern Illinois is a region generally covering the northern third of the U.S. state of Illinois. Northern Illinois is dominated by the metropolitan areas of Chicago, Rockford, and the Quad Cities, which contain a majority (over 75%) of Illinois' population and economic activity, including numerous Fortune 500 companies and a heavy manufacturing, commercial, retail, service, and office based economy. Much of the economic activity of the region is centered in the Chicago Loop, the Illinois Technology and Research Corridor, and the Golden Corridor. However, rural sections of this region are highly productive agriculturally, and are part of the Corn Belt.