Districts are the major administrative divisions of a state and are further sub-divided into smaller taluks.

During the British Raj, 12 districts of the erstwhile Madras Presidency had their boundaries within the present-day Tamil Nadu.

During the British Raj, the Madras Presidency was made up of 26 districts, 12 of which were part of the boundaries of the present-day Tamil Nadu, namely, Chingleput, Coimbatore, Nilgiris, North Arcot, Madras, Madura, Ramnad, Salem, South Arcot, Tanjore, Tinnevely, and Trichinopoly.

The princely state of Pudukottai acceded to the Indian Union on 4 March 1948 and was made as a part of the Trichinopoly district.

The Tamil speaking regions of Kanyakumari, which were earlier part of Travancore-Cochin, were merged to the Madras State.