The MIMAROPA Region, together with CALABARZON, were officially created with the partitioning of Region IV (Southern Tagalog) into the two regions by Executive Order No. 103 dated May 17, 2002, with 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, while Region IV-A was designated as CALABARZON.

On May 23, 2005, Executive Order 429 was issued moving the province of Palawan to the Region VI or the Western Visayas Region, effectively designating Region IV-B as MIMARO. However, Palawan residents criticized the move citing lack of consultation, with most residents in Puerto Princesa City and nearly all municipalities preferring to stay with Region IV-B.

Consequently, Administrative Order No. 129 dated August 19, 2005 was issued to hold in abeyance the implementation of Executive Order 429, pending the approval of an implementation plan for the orderly transfer of Palawan from MIMAROPA to Region VI.

However, the 2010 Philippine Census of Population still reported the region’s name as “MIMAROPA” and included Palawan as part of the region, and 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, with no boundary changes involved.

COA Regional Office No. IV-B was formally established on January 11, 2013.