Olympic National Forest is a U.S. National Forest located in Washington, USA. With an area of 628,115 acres (2,541.89 km2), it nearly surrounds Olympic National Park and the Olympic Mountain range. Olympic National Forest contains parts of Clallam, Grays Harbor, Jefferson, and Mason counties. The landscape of the national forest varies, from the temperate Olympic rain forest to the salt water fjord of Hood Canal to the peaks of Mt. Washington.
Annual precipitation averages about 220 inches (5.6 m), giving rise to streams such as the Humptulips River. Olympic National Forest was originally created as Olympic Forest Reserve in 1897, then renamed to Olympic National Forest in 1907. A 1993 Forest Service study estimated that the extent of old growth in the Forest was 266,800 acres (108,000 ha). It is administered in two ranger districts: the Pacific Ranger District on the west side of the Olympic Peninsula, and the Hood Canal Ranger District on the east side.