Triangle Lake is an unincorporated community in Lane County, Oregon, United States. It is about 25 miles west of Junction City on Oregon Route 36, on the southwest side of the lake of same name. Lake Creek, a tributary of the Siuslaw River, enters and exits the lake. Triangle Lake is closely linked to the unincorporated community of Blachly, on the northeast side of the lake, and the two communities share the K-12 Triangle Lake School, the only school in Blachly School District.