Chachoengsao is a town in eastern Thailand, due east of Bangkok, about 80 km distant.
Chachoengsao, Paet Rio, has a history dating back to the reign of King Borommatrailokkanat in the Ayutthaya period. Most people have settled by the Bang Pakong River and along canals. "Luangpho Phuttha Sothon" is a centre of faith of the people of Paet Rio. In the past, Chachoengsao was a fourth class city under the ministry of defence. During the reign of King Rama I, it was attached to the ministry of the interior. During the reign of King Rama V, who changed the administration system, Chachoengsao became a city in the Prachin Buri Circle. In 1916, its status was changed from a city to a province. "Chacheongsao" is a Khmer word which means "deep canal". The name "Paet Rio" comes from the story that the city once teemed with giant snakehead fish; up to eight cuts were required on the sides in the making of sun-dried fish.