Chatham County is a county in the U.S. state of Georgia, and is located on the states Atlantic coast. The county seat and largest city is Savannah. One of the original counties of Georgia, Chatham County was created February 5, 1777, and is named after William Pitt, 1st Earl of Chatham. The U.S. Census Bureaus 2015 population estimate for Chatham County was 286,956 residents, making Chatham the most populous Georgia county outside the Atlanta metropolitan area. In the official 2010 census, the population of Chatham County was 265,128. Chatham is the core county of the Savannah metropolitan area.