MIMAROPA Region, together with Calabarzon, were officially created with the partitioning of Region IV (Southern Tagalog) into the two regions on May 17, 2002 with the issuance of Executive Order No.
103 by then-President Gloria Macapagal-Arroyo; for the purpose of promoting efficiency in the government, accelerating social and economic development and improving public services in the provinces covered.
Region IV-B was designated as Mimaropa, which stands for the island provinces belonging to the Southern Tagalog region—Mindoro (Oriental and Occidental), Marinduque, Romblon and Palawan.
Region IV-A was designated as Calabarzon.

On May 23, 2005, Executive Order 429 was issued, moving the province of Palawan to the region of Western Visayas, designating Region IV-B as "Mimaro".
However, Palawan residents criticized the move, citing a lack of consultation, with most residents in Puerto Princesa and nearly all municipalities preferring to stay with Region IV-B. Consequently, Administrative Order No.
129 was issued on August 19, 2005 to address this backlash.
This order directed the abeyance of Executive Order 429 pending the approval of an implementation plan for the orderly transfer of Palawan from Mimaropa to Region VI.

The 2010 Philippine Census of Population reported the region's name as "MIMAROPA" and included Palawan as part of the region.
As of 2014, it is not clear whether the transfer of Palawan to Western Visayas is still considered pending by the Philippine government.
As of 2014, the National Statistical Coordinating Board of the Philippines continued to list Palawan province as part of the Mimaropa region.

On July 17, 2016, Republic Act No.
10879 formally established the Southwestern Tagalog Region to be known as the Mimaropa Region.
This involved no boundary changes but was in effect merely a renaming and discontinuation of the "Region IV-B" designation.
MIMAROPA Region, together with Calabarzon, were officially created with the partitioning of Region IV (Southern Tagalog) into the two regions on May 17, 2002 with the issuance of Executive Order No. 103 by then-President Gloria Macapagal-Arroyo; for the purpose of promoting efficiency in the government, accelerating social and economic development and improving public services in the provinces covered. Region IV-B was designated as Mimaropa, which stands for the island provinces belonging to the Southern Tagalog region—Mindoro (Oriental and Occidental), Marinduque, Romblon and Palawan. Region IV-A was designated as Calabarzon.
On May 23, 2005, Executive Order 429 was issued, moving the province of Palawan to the region of Western Visayas, designating Region IV-B as "Mimaro". However, Palawan residents criticized the move, citing a lack of consultation, with most residents in Puerto Princesa and nearly all municipalities preferring to stay with Region IV-B. Consequently, Administrative Order No. 129 was issued on August 19, 2005 to address this backlash. This order directed the abeyance of Executive Order 429 pending the approval of an implementation plan for the orderly transfer of Palawan from Mimaropa to Region VI.
The 2010 Philippine Census of Population reported the region's name as "MIMAROPA" and included Palawan as part of the region. As of 2014, it is not clear whether the transfer of Palawan to Western Visayas is still considered pending by the Philippine government. As of 2014, the National Statistical Coordinating Board of the Philippines continued to list Palawan province as part of the Mimaropa region.
On July 17, 2016, Republic Act No. 10879 formally established the Southwestern Tagalog Region to be known as the Mimaropa Region. This involved no boundary changes but was in effect merely a renaming and discontinuation of the "Region IV-B" designation.
Mimaropa