Jonesboro is a city in Clayton County, Georgia, United States. The population was 4,724 as of the 2010 census. The city is the county seat of Clayton County.The city's name was originally spelled Jonesborough. During the Civil War, the final skirmish in the Atlanta Campaign was fought here south of Atlanta, cutting off the city and forcing the mayor of Atlanta to surrender at Marietta in early September 1864.