Rainbow Falls State Park, State park in Lewis County, Washington, United States

Rainbow Falls State Park is a forested property along the Chehalis River in western Washington that offers hiking trails, camping sites, and picnic areas throughout its grounds. The landscape combines river access with wooded paths and open spaces for visitors to explore.

The Upper Chehalis people fished for lampreys at the falls before the land passed into private hands and served for a time as a community park. In 1933 the site was traded for other state lands, and Civilian Conservation Corps Company 1633 built the log structures and a footbridge, completing the grounds in 1935. In April 1934, 28 Black enrollees from Illinois were assigned to the camp and lived in segregated barracks.

The name comes from rainbows seen in the spray of the falls, though a second account credits a Dryad resident who served in the Army's Rainbow Division. The Upper Chehalis people fished for lampreys here. Since 1978 the park has been the finish line of the Pe Ell River Run, in which entrants build or buy craft and float down the Chehalis, riding over the remaining waterfall.

The park is open year-round and day use is free. Most facilities, including a campground with over 40 sites, picnic areas and 3 miles of trails, lie in the northern section; State Route 6 divides the park. A spur trail connects to the Willapa Hills Trail. The 7 miles of looping trails south of the highway are flat and not wheelchair accessible.

The falls are only 5 feet (1.5 m) high after the December 2007 flood, which destroyed the CCC-era wooden footbridge over the Chehalis River and caused $6.5 million in damage. The name is usually traced to rainbows in the spray, though another account credits a Dryad resident who served in the Army's Rainbow Division.