The St. Croix River is a tributary of the Mississippi River, approximately 164 mi (264 km) long, in the U.S. states of Wisconsin and Minnesota. The lower 125 mi (201 km) of the river forms the state line between Wisconsin and Minnesota.
It rises in the northwestern corner of Wisconsin, out of Upper St. Croix Lake in Douglas County, near Solon Springs, approximately 20 mi (32 km) south of Lake Superior. It flows south to Gordon, then southwest. It is joined by the Namekegon River in northern Burnett County, then encounters and forms the boundary between Minnesota and Wisconsin, flowing generally south, past St. Croix Falls, Wisconsin and Stillwater, Minnesota, the oldest settlement in Minnesota. It joins the Mississippi at Prescott, Wisconsin, approximately 20 mi (32 km) southeast of St. Paul, Minnesota.
The upper reaches of the river in Wisconsin below the St. Croix Flowage, 15 mi (24 km) downstream from its source, as well as the Namekagon River, are protected as the St. Croix National Scenic Waterway.
The lower 27 mi (43 km) of both sides of the river along the Minnesota-Wisconsin border are protected as part of the Lower St. Croix National Scenic Waterway. The protected area includes the Dalles of the St. Croix River, a scenic gorge, located near Interstate State Park, south of St. Croix Falls.
