The Rock River is a tributary of the Big Sioux River, about 144 miles (232 km) long,[3] in southwestern Minnesota and northwestern Iowa in the United States.

The river's name comes from a prominent rocky outcrop about 175 feet high (designated "The Rock" on Joseph Nicollet's 1843 map of the area) of reddish-gray Sioux Quartzite, about 3 miles (5 km) north of Luverne.

[4] The outcrop of quartzite is contained in Minnesota's Blue Mounds State Park.

In its upper course in Minnesota, the river collects the East Branch Rock River, about 15 miles (24 km) long, which flows for its entire length in Pipestone County.

In Iowa, it collects the Little Rock River just south of Doon.