Willow River is a river in St. Croix County, Wisconsin, United States and a tributary of the St. Croix River. Its headwaters are found near the village of Deer Park (near the northern border of the county) (). The river at one time dumped into the lower St. Croix river in between Hudson and North Hudson (). But a dam was built to block off its mouth, a narrow channel was cut above the dam to the St. Croix River, the channel was dammed, and a mill was built to exploit the head of water that the two dams created.[1] Subsequently, the Willow River Power Co. built a hydroelectric facility to utilize the same head of water, but the head was substantially decreased when the United States built the Red Wing Dam 30 miles downstream on the Mississippi River.[1]
The river lazily winds back and forth with a slow flowage. Its origin is in and around the Cylon Wildlife Area. It passes south of Deer Park about one mile. It then passes through the towns New Richmond, Boardman, and Burkhardt. Near Burkhardt it inters the Willow River State Park.
The river is hardly canoed north of the town of Burkhardt due to fallen trees and sand bars. In times of low water it is nearly impossible to canoe the river. In the spring the high water in about 6 ft higher than the summer mean. Although it is possible to canoe or kayak the river is not advised. Trout fishing is general done down river from Boardman.
The status of the Willow River as a non-navigavble stream figured in constitutional litigation over whether a head of water to which it contributed was a property interest for purposes of the Fifth Amendment, in United States v. Willow River Power Co.