Chiayi County is bordered by Mount Yu to the east, Taiwan Strait to the west, Tainan City to the south and Yunlin County to the north. It spans over 1903 km2, which is about 5.35% of the total area of Taiwan. Due to its location on the Tropic of Cancer, Chiayi County has a unique landscape compared to other regions of Taiwan.

Chiayi County is divided into 2 cities, 2 urban townships and 14 rural townships. Taibao City is the seat of Chiayi County and is home to the Chiayi County Government. The Chiayi County Council, however, is located in Puzi City. The incumbent Magistrate of Chiayi County is Helen Chang, of the Democratic Progressive Party.

In December 2014, the population of Chiayi County numbered 524,783 people.