Decatur, GA has a population of 21,210 and is the 2,050th largest city in the United States. The population density is 4,782 per sq mi which is 2765% higher than the Georgia average and 5178% higher than the national average. The median age in Decatur is 35 which is approximately 3% lower than the Georgia average of 36. In Decatur, 55% of the population over 15 years of age are married, 88% speak English and 3% speak Spanish. 42% of Decatur residents were born in Georgia, 47% were born out of state, 2% were born outside of the United States and 9% were foreign born.