Tarn-et-Garonne is not one of the original 83 departments created during the French Revolution on 4 March 1790. It was created on 4 November 1808 during the First French Empire by Napoleon I.
It was formed out of territories belonging to neighboring areas. More than half of the territory was taken from the Lot (including Montauban and
Moissac), over one-third was taken from Haute-Garonne (including Castelsarrasin), and the rest from the departments of Lot-et-Garonne, Gers, and Aveyron.
The new department had three arrondissements: Montauban, Castelsarrasin and Moissac. The prefecture was Montauban. On 10 September 1926, the arrondissement of Moissac was eliminated.