When it was originally established in 1961 as a wildlife sanctuary the Mara covered only 520 square kilometres (200 sq mi) of the current area, including the Mara Triangle. The area was extended to the east in 1961 to cover 1,821 km2 (703 sq mi) and converted to a game reserve. The Narok County Council (NCC) took over management of the reserve at this time. Part of the reserve was given National Reserve status in 1974, and the remaining area of 159 km2 (61 sq mi) was returned to local communities. An additional 162 km2 (63 sq mi) were removed from the reserve in 1976, and the park was reduced to 1,510 km2 (580 sq mi) in 1984.
In 1995, the TransMara County Council (TMCC) was formed in the western part of the reserve, and control was divided between the new council and the existing Narok County Council. In May 2001, the not-for-profit Mara Conservancy took over management of the Mara Triangle.