The Rock River is a tributary of the Mississippi River, approximately 285 miles (459 km) long, in the U.S. states of Wisconsin and Illinois.

It rises in southeast Wisconsin, in southwest Fond du Lac County, approximately 10 miles (16 km) south of Ripon and 25 miles (40 km) southwest of Lake Winnebago. It flows south, through the Horicon National Wildlife Refuge , then meanders southward draining the area of southeast Wisconsin between the Wisconsin River and Lake Michigan. It passes Watertown, Jefferson, and Fort Atkinson. In northern Rock County it receives the Yahara River , and flows southward past Janesville and Beloit into northern Illinois, where it receives the Pecatonica River 5 miles (8 km) south of the state line.

It flows south through Rockford, then southwast across northwestern Illinois. passing Oregon, Dixon and Rock Falls, where it becomes navigable. It joins the Mississippi at Rock Island.

The Rock River is the public source of most drinking water in the towns, but has high levels of radon in it, and while residents are told it is harmless to drink, local Jefferson School has shut down its drinking fountains and provides all students with bottled water.

See also

• List of Illinois rivers
• List of Wisconsin rivers
• Ronald Reagan