Rock River, c.285 mi (460 km) long, rising in SE Wisc. and flowing SW through NW Ill. to the Mississippi River near Rock Island. It flows through a fertile farm area. Rockford, Ill., is the chief city on the river. Lake Koshkonong (c.20 sq mi/50 sq km) is a natural widening of the river.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.