[1] The plebiscite was held concurrently with the 1965 Philippine general election and the results were announced on February 15, 1966.

A previous division between Samar and Leyte occurred in 1747 but was reversed in 1762 due to Jesuit complaints, with final approval coming from the King of Spain.

In 1777, Samar and Leyte were split for the last time when it was approved in Madrid in 1786 and became effective in 1799; Queen Isabella II of Spain later officially declared Samar as a province in 1841.

4221 was passed on June 19, 1965, for such purpose, during the term of President Diosdado Macapagal.

[2] However, the last governor of undivided Samar, Esteban Piczon, had continued as the first governor of Western Samar from 1965 to 1967, while incumbent Samar representatives—Eladio Balite (1st district), Fernando Veloso (2nd district) and Felipe Abrigo (3rd district)—had already been re-elected for the newly created lone districts of Northern, Western, and Eastern Samar, respectively, concurrently with the 1965 plebiscite ahead of the 6th Congress.