Marietta is a city located in central Cobb County, Georgia, United States, and is its county seat. As of the 2010 census, the city had a total population of 56,579, making it one of metro Atlanta's largest suburbs. Marietta is the third-largest of three principal cities (by population) of and is included in the AtlantaSandy SpringsMarietta, Georgia, metropolitan statistical area, which is included in the Atlanta-Sandy Springs-Gainesville, Georgia-Alabama (part) combined statistical area. One story is the city was named for Mary Cobb, the wife of U.S. Senator and U.S. Supreme Court justice Thomas Willis Cobb.