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.
Over time, the lake has been referred to by various names, such as Loon Lake, Lake of the Woods, and Echo Lake. However, it was eventually given a permanent name, Triangle Lake, which reflects its distinctive triangular form, in the early 1900s.