The  lake has had various names over the years, including Loon Lake, Lake of the Woods, and Echo Lake, but the name Triangle Lake (after the lake's shape) became the official name in the early 1900s.
The lake has undergone several name changes over the years, including Loon Lake, Lake of the Woods, and Echo Lake, but it ultimately settled on the name Triangle Lake due to its geometric shape, which became official in the early 1900s.