Region XII or Central Mindanao was created last July 7, 1975, under Presidential Decree No. 742. This decree stated that Central Mindanao was composed of five (5) provinces and three (3) cities, namely: Cotabato, Sultan Kudarat, Lanao del Norte, Lanao del Sur and Maguindanao and the cities of Cotabato, Iligan, and Marawi. In August 1, 1989, Republic Act No. 6734 was signed into law, providing for the creation of the Autonomous Region in Muslim Mindanao (ARMM). The provinces of Lanao del Sur and Maguindanao were included in the composition of ARMM.
On October 12, 1990, Executive Order No. 429 was signed into law, defining the new composition of Central Mindanao with Koronadal City as its Regional Administrative Center. However, a restraining order was issued, resulting to the non-execution of the said EO. Thus, the composition of Region XII prior to the issuance of EO 429 (i.e. Cotabato Province, Sultan Kudarat, Lanao del Norte, Cotabato City, Iligan City, and Marawi City) remained on status quo. Cotabato City remained as the Regional Administrative Center of Region XII. It has been likewise designated as the temporary regional center of the ARMM.
On August 14, 2001, pursuant to the provision of RA 9054, a plebiscite was conducted in the Special Zone of Peace and Development (SZOPAD) to determine the areas that shall comprise the ARMM. The cities of Marawi in Region XII and Isabela in Region IX joined the ARMM. As a result of the reconfiguration of the ARMM, Pres. Gloria Macapagal-Arroyo issued Executive Order No. 36 dated September 19, 2001, which calls for the realignment of the regions in Mindanao. The province of Lanao del Norte and Iligan City of Region XII were transferred to Region X. The provinces
of South Cotabato, Sarangani, and the cities of Koronadal and General Santos of Region XI became part of the new Region XII.
Thus, per Executive Order No. 36 dated September 19, 2001, “Providing for the Reorganization of the Administrative Regions in Mindanao and for other purposes”, Region XII now is called “SOCCSKSARGEN” and is composed of 4 provinces and 5 cities. These provinces are: North Cotabato, Sarangani, South Cotabato, and Sultan Kudarat. The five cities are: Cotabato City, Koronadal City, Gen. Santos City, Kidapawan City and Tacurong City. Only two cities are considered chartered cities namely: Cotabato City and General Santos City. Kidapawan City, Koronadal City, and Tacurong City are considered component cities of North Cotabato, South Cotabato, and Sultan Kudarat provinces respectively. Sarangani, and the cities of Koronadal and General Santos of Region XI became part of the new Region XII.