Lake Wilderness Arboretum, Botanical garden in Maple Valley, Washington, United States.

Lake Wilderness Arboretum is a 40-acre (16 ha) arboretum in Maple Valley, Washington, off the Lake Wilderness Trail. It focuses on Northwest native plants and holds one of the world's largest collections of Western Azalea (Rhododendron occidentale), with over 200 selections of the species.

The arboretum was first established as a nonprofit organization in 1965, and its initial design was completed and implemented in 1970. The City of Maple Valley finalized the transfer of Lake Wilderness Park and the Arboretum from King County in January 2003. In April 2003, the name was changed from South King County Arboretum to Lake Wilderness Arboretum, and the foundation took its current name in 2007.

The arboretum's name comes from Lake Wilderness Park, from which the City of Maple Valley took over the grounds in January 2003; the site had been called South King County Arboretum until April 2003. The Western Azalea Garden, dedicated in June 2000, holds over 200 selections of Rhododendron occidentale, a collection visitors can walk among.

The garden is open daily from sunrise to sunset with free entry and parking near the main entrance. Wear sturdy shoes for walking the trails, as wooded paths can be muddy or slippery depending on recent weather.

The arboretum holds one of the world's largest collections of Western Azaleas, with over 200 different varieties that bloom in spring. This specialized collection draws visitors who come specifically to see the colorful flowering display during the growing season.