Forsyth County is a county located in the U.S. state of Georgia. As of the 2010 census, the population was 175,511. The county seat is Cumming.Forsyth County is included in the Atlanta-Sandy Springs-Roswell, GA Metropolitan Statistical Area.Forsyth County has been one of the fastest growing areas in the United States in terms of percentage of growth for several years during the 2000s.