Tainan County was established on 7 January 1946 on the territory of Tainan Prefecture (臺南州) shortly after the end of World War II.

The remaining Tainan County has territory equivalent to the Shin'ei (Hsinying), Niitoyo (Hsinfeng), Shinka (Hsinhua), Sobun (Tsengwen), and Hokumon (Peimen) in the Japanese era.

In addition, districts in the remaining part of Kaohsiung County was defunct.

On 25 December 2010, the county merged with Tainan City to form a larger single special municipality.

On the eve of merging with Tainan City, the county consists of the following administrative divisions