Phatthalung is one of the southern provinces of Thailand. Neighboring provinces are (from north clockwise) Nakhon Si Thammarat, Songkhla, Satun and Trang. Phatthalung was formerly known as Mardelong in Malay, especially during the time when the region came under Muslim influence.
During the reign of King Ramathibodi I of the Ayutthaya kingdom in the 14th century Phatthalung became one of twelve royal cities. At the end of the 18th century King Rama I submitted the city to the Ministry of Defense, which was responsible for all the southern provinces. During the administrative reform by King Chulalongkorn Phatthalung became part of the Monthon Nakhon Si Thammarat.
The province is located on the Peninsula Malaysia. To the east it borders the large shallow Songkhla lake, while the west is covered by mountains of the Nakhon Si Thammarat chain. The Khao Pu - Khao Ya National Park is located in these mountains at the border to Trang.