Rockford is a mid-sized city located on both banks of the Rock River

Rock River (Illinois)

The Rock River is a tributary of the Mississippi River, approximately long, in the U.S. states of Wisconsin and Illinois. It rises in southeast Wisconsin, in the Theresa Marsh near Theresa, Wisconsin in northeast Dodge County, Wisconsin approximately south of Fond du Lac, Wisconsin...

 in far northern Illinois

Illinois

Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...

. Often referred to as "The Forest City", Rockford is the county seat of Winnebago County, Illinois

Winnebago County, Illinois

Winnebago County is a county located in the U.S. state of Illinois. According to the 2010 census, it has a population of 295,266, which is an increase of 6.1% from 278,418 in 2000...

, USA. As reported in the 2010 U.S. census, the city was home to 152,871 people, the third most populated city in the state behind Chicago and Aurora

Aurora, Illinois

Aurora is the second most populous city in the U.S. state of Illinois, and the 112th largest city in the United States. A suburb of Chicago, located west of the Loop, its population in 2010 was 197,899. Originally founded within Kane County, Aurora's city limits have expanded greatly over the past...

. The metropolitan area

Rockford metropolitan area

The Rockford Metropolitan Statistical Area, as defined by the United States Census Bureau, is an area consisting of two counties in north-central Illinois, anchored by the city of Rockford. As of the 2000 census, the MSA had a population of 320,204...

 has 339,178 residents as of the 2000 census. During the latter part of the 20th century Rockford was the second largest city in Illinois and is currently the most populated city in Illinois outside of the Chicago Metropolitan Area.