History and Giving Context for Atlanta Demographics - adding numbers to population chart
While Fulton County did not encompass all of what is in the Atlanta SMSA today, I think it is misleading to provide only Atlanta City population numbers in the mid-19th c. While it was established as a railroad terminus, it didn't exist by itself.

In 1860 Fulton County had a total of 14,427 people.  There were 2955 enslaved African-Americans, 20.5% of the population.  While much of north GA had mostly yeoman farmers, both Cobb and Fulton County also had planters (defined by historians as holding 20 or more slaves), who held slaves for labor on large cotton plantations. 

(I know more about Roswell in Cobb county, than Fulton, but the origins of major planters and the slaves they brought with them are likely similar. Roswell King and planters he invited to join him in his enterprise (at what became Roswell) were from the coast. King brought 36 slaves from his coastal plantation and bought another 42 at Darien, GA, to take with him to work on building his house, the mill, and supporting buildings. Archibald Smith brought 36 slaves with him from his coastal plantations in St. Marys County and created a 300-acre cotton plantation in Roswell. King's idea was to have cotton production AND  processing in the same place. The forced migration of slaves from the coast to north GA meant they brought their unique Geechee culture and language with them.  Where slaves were held in larger numbers on plantations, it's likely they kept their culture and traditions going.) 

Atlanta and Fulton County in fact more than doubled in population from 1860 to 1870. People rushed to rebuild the city.  In a pattern typical of other areas, many newly freed African-Americans left plantations to move to town to work at trades or crafts, to have safety in numbers and to try to set up lives apart from white control.  

By 1870 Fulton County had grown to 33,446 people.  Among them were 15,282 "colored", as defined by the census, 45.7% of the population. 

NOTEWORTHY CITIZENS: Atlanta boasts two Nobel Prize winners: Rev. Martin Luther King, the youngest man to receive the Nobel Prize, and President Jimmy Carter.  Each were awarded the Nobel Prize for Peace.