William O'Brien State Park is an 1880-acre park located on Saint Croix River. The daughter of a local lumber baron, William O'Brien, donated land for the park. The park is about an hour drive from the Minneapolis/Saint Paul metropolitan area. The park has a diverse landscape which includes the Saint Croix River, wetlands, hilly hardwood forests, and prairies. William O'Brien State Park offers a wide variety of outdoor activities from hiking to canoeing to winter recreation.

The park has 16 miles of hiking trails; most of these trails are groomed for cross country skiing in the winter. There is a swimming beach as well as fishing dock at Lake Alice. One can also fish the St. Croix River. Canoe, kayak, and paddleboard rentals are available. There is a large picnic area near Lake Alice.

The park has a visitor’s center with interpretive exhibits. There are also naturalist programs during the warm months.

There are two campgrounds (one is right by the river) at the park with a total of 125 sites, of which 71 have electric hook ups. In addition, there are 4 group camping areas and 4 camper cabins.