In the Middle Ages the present area of the Tomaszów Lubelski county formed a part of Grody Czerwieńskie, an area causing arguments and fights between Poland and Russia. Only in 1366 king Kazimierz Wielki incorporated the region into Poland. Duchies of Bełżec and Chełm, making up Grody Czerwieńskie, returned within the borders of Poland in 1462. It was then that the former received a province status, and the latter was included into the ruskie province with the seat in Lviv. The area of the former Tomaszów country persisted within the limits of the bełskie (Bełżec) province until the 1st partition of Poland, i.e. until 1772.

The lubelskie province with the Tomaszów county was among the first five provinces with borders determined immediately in 1919 by authorities of independent Polish state. In 1944 the Tomaszów county was reactivated with the area enlarged by incorporation if communes: Bełżec, Lubycza Królewska and Tarnoszyn. It bordered then the Zamość county in the north, the Biłgoraj county in the west, the Lubaczów county in the suoth and the Hrubieszów county in the north-east. Its south-eastern border was at the same time also the national border. After the administrative reform of Poland conducted in 1975 the whole area of the liquidated county was included within the newly arisen zamojskie (Zamość) province. Only the new administrative division introduced on 1 January 1999 restored the Tomaszów Lubelski county.