Mongkol Borey ( ) is a district (srok) in the south of Banteay Meanchey Province, in northwestern Cambodia. The district capital is the town of Mongkol Borey, around nine kilometres south of the provincial capital of Serei Saophoan by road. The district shares a border with Battambang Province to the south. The main railway line from Phnom Penh to Poipet on the border with Thailand runs through the district from north to south. The district is easily accessed by road from Serei Saophoan (9 km) Battambang (60 km), and Siem Reap (110 km). Mongkol Borey district is one of the smallest districts in Banteay Meanchey Province by area and only Serei Saophoan Municipality is smaller. However, it has the largest district population in the province due to its central location and transport infrastructure. National Highway 5 which begins in Phnom Penh and ends at Poipet and the National railway bisect the district in parallel running from north to south. National road 160 begins near the centre of the district and runs southwest into Pailin. History The history of Mongkol Borey District before the 18th century is unclear, although it is likely that it was part of Battambang province. However, the first record of the city was first mentioned in the chronicle of Rama III of Siam that the city was established in 1833 and was first assigned to Ang Duang. From the 18th century until 1907, it was part of Phra Tabong province of Thailand. At that time the Siamese controlled the area that is modern Banteay Meanchey, Oddar Meanchey, Siem Reap, Pailin and Battambang Provinces. Under the French-Siamese treaty of 23 March 1907, these parts of Cambodia were returned. At this time the area around Serei Sophorn was part of Serei Sophorn District of Battambang. Between 1925 and 1940 a number of new Battambang districts were created, including Mongkol Borey. In 1988 the five northern districts of Battambang were separated to form the new province of Banteay Meanchey. It is the birthplace of King Sisowath (then part of Battambang province) who was King of Cambodia from 1904 to 1927. Location Mongkol Borey district lies in the south of the province and shares a border with Battambang Province. From the north clockwise, Mongkol Borey borders Serei Saophoan District to the north. The eastern border of the district is shared with Preah Netr Preah district. The Mongkol Borey River forms part