Hartford is a village in Madison County, Illinois, United States, on the Mississippi River near the mouth of the Missouri River. The population was 1,429 at the 2010 census. Lewis and Clark spent the winte…Hartford is a village in Madison County, Illinois, United States, on the Mississippi River near the mouth of the Missouri River. The population was 1,429 at the 2010 census. Lewis and Clark spent the winter of 1803-1804 there, near what has been designated the Lewis and Clark State Historic Site.