State Route 100 (SR 100) is a 4.68-mile-long (7.53 km) state highway in the U.S. state of Washington, serving Cape Disappointment State Park in Pacific County. The highway travels counterclockwise from U.S. Route 101 (US 101) in Ilwaco south to Cape Disappointment and north to an intersection with itself in Ilwaco. SR 100, part of the Lewis and Clark Trail Scenic Byway, serves as a loop route and has a spur route that serves the state park and a Coast Guard station.