Chachoengsao (ฉะเชิงเทรา, t͡ɕhàʔ.t͡ɕhɤ̄ːŋ.sāw) is one of Thailand's seventy-six provinces (changwat), located in eastern Thailand.
Chachoengsao or Paet Rio ('eight stripes') is a province in eastern Thailand. It has a history dating back to the reign of King Borommatrailokkanat in the mid-Ayutthaya period. People originally settled by the Bang Pakong River and along canals. 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. "Chachoengsao" is a Chong 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.
Neighboring provinces are (from north clockwise) Prachinburi, Sa Kaeo, Chanthaburi, Chonburi, Samut Prakan, Bangkok, Pathum Thani, and Nakhon Nayok. It has a short coastline on the Gulf of Thailand.
The western part of the province is the low river plain of the Bang Pa Kong River, which is used extensively for farming rice. To the east is hillier terrain, with an average elevation of more than 100 metres. In Tha Takiap District is the Khao Ang Rue Nai Wildlife Sanctuary with an area of 674,352 rai ~ . The total forest area in the province is or 15.5 percent of provincial area.
The province has gained a reputation as a centre for recycling potentially hazardous electronic waste (e-waste), despite a June 2018 ban on imports of foreign e-waste to Thailand. China banned the import of foreign e-waste in 2018 also.