Rockford, Illinois is 53% larger than South Bend, Indiana.
Area: 166 km2 calculated
Rockford is the third largest city in the U.S. state of Illinois, the 160th most populous city in the United States, and the 112th most populous region in the United States. It is the county seat of Winnebago County and is located on both banks of the Rock River in far northern Illinois. Wikipedia
Area: 109 km2 calculated
The city of South Bend is the county seat of St. Joseph County, Indiana, United States, on the St. Joseph River near its southernmost bend, from which it derives its name. Wikipedia