Decatur, TN has a population of 1,429 and is the 12,980th largest city in the United States. The population density is 376 per sq mi which is 146% higher than the Tennessee average and 316% higher than the national average. The median age in Decatur is 46 which is approximately 18% higher than the Tennessee average of 39. In Decatur, 68% of the population over 15 years of age are married, 99% speak English and 0% speak Spanish. 70% of Decatur residents were born in Tennessee, 29% were born out of state, 0% were born outside of the United States and 1% were foreign born.