Walnut Woods State Park is a state park in Polk County, Iowa, United States, located in suburban West Des Moines. Within the Des Moines metropolitan area, the park preserves a bottomland hardwood forest featuring the largest natural stand of black walnut trees in North America. The Raccoon River meanders through the 260 acre park, providing fishing and canoeing opportunities. The park also provides picnic areas, a limestone lodge built in the 1930s, and a small campground with 22 sites. More than 90 bird species have been seen in the park.