During the Ayutthaya era and under the reign of King Naresuan, Trat province (within which Koh Chang lies) was originally called Baan Bang Pra. The present-day name Trat is often said to be named after a tree which can be found in abundance throughout the area and is commonly used to make brooms. Called the ‘Krat’ tree, the name over the years likely formed the basis for the present name ‘Trat’.

Trat province played an important role during negotiations with France when Rama V was in power. Originally the area was handed over to the French in an agreement that would see the removal of French troops from Chantaburi Province. However the Rama later managed to reclaim Trat when on March 23, 1906 the French handed it back in exchange for the areas Sri Sophon, Pratabong and Siem Reap. Seen as a victory for Thailand, the residents of Trat built the Rama V Monument which can be seen at the City Hall and even to this day they celebrate March 23 as their ‘Independence Day’ and organise the ‘Trat Recalling Day’ every year to remember these events and the King who saved Trat from foreign rule.

The area again came under siege from the French during the Indochina War when on January 17, 1941 the French Navy crossed into Thai waters and a fierce battle with Thai ships ensued. Whilst the Thais won and were successful in driving away the French, the war which has since been called the ‘Koh Chang Naval Battle’ laid claim to numerous Thai lives as well as the three Thai battleships ‘Songkhla’, ‘Chonburi’ and the ‘Thonburi’. As a mark of respect for those who lost there lives fighting for their country the Thai Navy holds a merit-making ceremony each year on January 17.