| Rock River | |
| Pushpin Map: | Iowa |
| Pushpin Map Caption: | Mouth |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | Iowa, Minnesota |
| Subdivision Type4: | District |
| Subdivision Name4: | Sioux County, Iowa, Lyon County, Iowa, Rock County, Minnesota, Pipestone County, Minnesota |
| Discharge1 Location: | Rock Valley, Iowa |
| Discharge1 Avg: | 610 cu/ft. per sec.[1] |
| Source1 Coordinates: | 44.1369°N -96.1231°W |
| Mouth: | Big Sioux River |
| Mouth Coordinates: | 43.0827°N -96.4545°W |
| Mouth Elevation: | NaN460744}}</ref> |
| Tributaries Left: | Champepadan Creek |
The Rock River is a tributary of the Big Sioux River, about long,[2] in southwestern Minnesota and northwestern Iowa in the United States. Via the Big Sioux and Missouri rivers, it is part of the watershed of the Mississippi River. 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.[3] The outcrop of quartzite is contained in Minnesota's Blue Mounds State Park.
The Rock River starts in Pipestone County, Minnesota, approximately northeast of the town of Pipestone, and flows initially southwardly through Rock County, Minnesota, and Lyon County, Iowa, where it turns southwestward into Sioux County, Iowa. It flows into the Big Sioux River in Sioux County, 6miles north of Hawarden.
Along its course the Rock River passes the towns of Holland, Edgerton, Luverne and Ash Creek in Minnesota; and the towns of Rock Rapids, Doon and Rock Valley in Iowa.
In its upper course in Minnesota, the river collects the East Branch Rock River, about long, which flows for its entire length in Pipestone County. In Iowa, it collects the Little Rock River just south of Doon.