William O’Brien State ParkPosted on March 24, 2016 by Unny Nambudiripad Loading Map.... William O’Brien State Park 16821 O'Brien Trail North - Marine on St. Croix 16821 O'Brien Trail North , Marine on St. Croix, MN, 55047 45.2250941 -92.7605547 Address 16821 O'Brien Trail North Marine on St. Croix MN 55047 United States Upcoming Events No events in this location Tweet