Chatham County is a county located in the U.S. state of Georgia. The county seat and largest city is Savannah. The U.S. Census Bureau’s 2011 population estimate was 271,544 residents. (The 2010 census reported a total population of 265,128, a 14.3 percent increase over the 2000 figure of 232,048. ) Chatham is the most populous Georgia county outside the Atlanta metropolitan area.