In 1855 (Hulsakrach 1217), which was the fifth year of the reigning of King Rama IV of Krung Rattanakosin, the king had established Koh Kong, former a part of Trat, as a new city, as stated in the Royal Decree on Tuesday, the waxing gibbous of the eighth lunar month, Tho (Rabbit year) Sapatasok, a special year of which last number is 7, that :

         Muang Prachanta khirikhet, which was variably mentioned as Muang Prachanta khirikhet or Prajanpa Khirikhet in most Thai historical texts. The city was established to be a counterpart city of Prachuab Khirikhan as they were situated on the same latitude. King Rama IV had been studying the science of Astronomy and was able to calculate Solar Eclipse precisely. For that matter, the King was aware of the importance of strategies to defend the Gulf of Siam. Therefore, Prachanta Khirikhet was later developed to be a naval station by Siam’s Bureaucracy.

         Later, Siam found itself in conflict with France in R.S. 112. The French navy seized Chantaburi on 19th August 1893 to coerce Siam to comply with its demands to exploit the opportunities as much as possible. The negotiation over the reclamation of the control over Chantaburi was prolonged until the mid-September 1902. France proposed that some of the coastal cities of Siam, including Trat, Koh Chang, Koh Kong, Phra Tabong, and Siem Rat, should be ceded to it, but the proposition was declined by Siam. France proposed the demand again for Siamese cession of Trat and Koh Kong, instead of Chantaburi.

         Finally, Siam had to cede Trat and Prachanta khirikhet, resulting in France’s demilitarization from Chantaburi. France could perceive that Thai was unease of losing Trat, and it wasn’t pleased with the notion of taking Trat as its protectorate as it is not worth France’s expense and investment. France, later, asked to exchange Trat for Monton Burapha (East territories) of Siam. The treaty was signed and Siam government was forced to cede Battambang, Siem Reap, and Srisophon, in exchange of France returning Siam Trat and other islands, the areas starting from Laem Ling to Koh kood. It can be perceived that while giving back the control over Trat, France didn’t return that over Prachanta khirikhet, which was ceded along with Trat; therefore, the claims over Prachanta khirikhet or Koh Kong have not been returned to Thailand since then.