Union County was established on July 7, 1870, during the post-Civil War Reconstruction era, from portions of Tippah, Lee, and Ponotoc counties. Governor James L. Alcorn appointed Union County's first officials and set New Albany as the county seat. The first courthouse was built on Cotton Street circa 1870, and the current courthouse was constructed in 1909. According to local legend, the county was named for Union District, South Carolina, where a number of the county's settlers originated.