Chatham is a village in Sangamon County, Illinois, United States. It is located 2.8 miles south of Springfield and has a retail trade area that extends into four other municipalities, including Springfield. The population was 11,500 as of the 2010 census and estimated to be 11,946 as of 2012. The village lies along the original alignment of historic U.S. Route 66.Chatham is part of the Springfield, Illinois Metropolitan Statistical Area.