The name Barangay Sum-ag originated at the time when the island of Negros was yet inhabited by uncivilized people known as Aetas who lived right at the place where the source of Sum-ag River is situated. This place was called "SAMAC". The reason advance by this group of people was that the two source of the river met at this point thereby creating in one river. But the Aetas being wandering type of people found that a little distance farther than the place where the source of river met, the opening was bigger. For this reason, they gave another name to the river "SUMMAG". But this did not stop them; it flows further and found its opening at the seashore. In the meanwhile, the population of the civilized people near the outlet of this river grew in number, which consequently enhanced the bad relationship between the civilized tribe. Consequently while the upper tribe called the place "SUMMAG", the lower tribe had to call it "SUM-AG". Finally the place was called "SUM-AG".

 

The Barangay Sum-ag was founded in the year 1780 as shown in the diary of Don Andres Claridad, Sr. amd was made a regular town sometime in November 1920. However when a petition of the municipalities of Bacolod, Murcia and Bago was initiated in 1902, it reverted to its Barangay status.