The district of Chiayi is located in the west of the island of Taiwan, between the county of Yunlin in the north and the city of Tainan in the south. In the west, it borders the Formosastraße, the north-east to the district Nantou and the southeast to the city Kaohsiung.

The western part of the county belongs to the Jianan Plain, the largest plains in Taiwan. In the east, the Alishan Mountains, which is touristic through the Alishan Forest Railway. At its eastern tip, the county of Chiayi reaches as far as the Yushan.

The northern turning point, which is the border between the subtropical and the tropical climatic zone, runs through the county of Chiayi.