Decatur is the county seat of Wise County, Texas, United States. Its population was 6,538 in 2020. Wise County was established in 1856…Decatur is the county seat of Wise County, Texas, United States. Its population was 6,538 in 2020. Wise County was established in 1856, and Taylorsville was made the county seat. Absalom Bishop, an early settler and member of the Texas Legislature, opposed naming the town after a Whig Party member, and in 1858, arranged to have the name changed to Decatur, in honor of naval hero Stephen Decatur.