Sisophon was a changwat (province) of Thailand. In 1906 it was ceded to French Indochina. It is now part of Cambodia and known as Banteay Meanchey.
During the 16th Century and beyond, Sisophon was known as Srey Saophoan meaning in Khmer "Beautiful Lady" and it was a small district, belonging in Battambang Province.
Onward to the 17th century, the Siamese later known to the world as Thai, took over Battambang Province, Siem Reap Province in a successful military campaign.
Battambang Province and Siem Reap province was renamed as Phra Dambang and Siam Nakorn respectfully. Therefore, Srey Saophoan was renamed as Srisophon in the Siamese/Thai language.
When the French imperialists came in the 1900s, the Siamese were forced to cede Battambang Province and Siem Reap Province back to Cambodia.
So the name of these province were changed back to their Khmer names. Srisophon was changed officially back to Serey Saophoan meaning in Khmer "Beautiful Freedom" as implying freedom from the Siamese control for a long time of nearly 200 years.
After the Khmer Rouge reign, Battambang Province was broken up into two provinces. Those provinces are the remaining Battambang Province and Banteay Meanchey Province.
Sisophon was made the capital city of Banteay Meanchey Province.