The county covered 2836 km2 and was located in the central part of Greater Romania, in the south of Transylvania.

The territory of Târnava-Mare County was transferred to Romania from the Kingdom of Hungary as successor state to Austria-Hungary in 1920 under the Treaty of Trianon.

In 1940, a portion of the county was transferred back to Hungary with the rest of Northern Transylvania under the Second Vienna Award.

Beginning in 1944, Romanian forces with Soviet assistance recaptured the ceded territory and annexed it to the rump county.

According to the 1930 census, the county counted 147,994 inhabitants, of which 44.8% were Romanians, 39.7% Germans, 11.8% Hungarians, 2.6% Romanies, and other smaller minorities.