The American civilian government in the Philippines implemented nationwide reorganization of political units. On June 1, 1903, Governor William Howard Taft signed Act No. 787 which called for the creation of the Moro Province composed of Cotabato, Davao, Lanao, Sulu, and Zamboanga Districts. Then on September 1, 1914, Governor Francis Burton Harrison approved Act No. 2408 otherwise known as the Organic Act for the Department of Mindanao and Sulu. Act No. 2408 also created the Province of Cotabato (CHAPTER II – THE PROVINCIAL GOVERNMENTS. ARTICLE 8 – PRELIMINARY PROVISIONS. Sec. 19. The provinces. Sub-section C).
President Ferdinand E. Marcos signed into law Republic Act No. 4849 on July 18, 1966. “The municipalities of Norala, Surala, Banga, Tantangan, Koronadal, Tupi, Polomolok, Kiamba, Maitum, Maasim, Tampacan and Glan and the City of Rajah Buayan (General Santos) are hereby segregated from the Province of Cotabato and constituted into a separate province to be known as South Cotabato” (Section 1). The municipality of Koronadal was named as the capital (Section 3).
When President Corazon C. Aquino approved Republic Act No. 7228 on March 16, 1992 thereby creating the province of Sarangani, the municipalities of Alabel, Glan, Maasim, Maitum, Malapatan, Malungon, and Kiamba were carved out of the Province of South Cotabato.