The District was captured by Portugese in the 16th century. The destruction and looting of the Koneswarar Temple by Constantine De Saa on a New Year day in the beginning of 1620 was a turning point in the history of the District. The Dutch conquered this district from Portugese in 1693 and it fell into the hands of British in 1796.
By a Proclamation of 01/10/1833 when the country was demarcated into five provinces for purpose of administration, Trincomalee District formed part of the Eastern Province. Until 1953, except for occasional changes the District boundaries remained unchanged. Until 1958 the District was administered by an Assistant Government Agent under the Government Agent of the Eastern Province in Batticaloa.
From August 1972, Thennamaravadi (31E) and Pulmoddai (31G) Gramasevaka Divisions of Kuchchaveli A.G.A. Division and Parana Madawachchiya (31F) Gramasevaka Division of Gomarankadawala A.G.A. Division were detached from Trincomalee District and attached to Pdaviya A.G.A. Division of Anuradhapura District. Subsequently, Padavi Siripura (31D), Thennamaravadi (31E), Parana Madawachchiya (31F) and Pulmoddai (31G) G.S. Divisions of Padaviya A.G.A. Division were attached to Trincomalee District with effected from 13th May 1982. As the A.G.A. Divisions were increasing, the internal boundaries of the A.G.A. Divisions were subjected to changes from time to time.
Trincomalee District has a population of 412,432; the ethnic composition is Muslim 41% Tamil 35% and Sinhalese 24 %.