48px-Wikipedia-logo-v2.svg.png Wikipedia has an article on Cairo, Illinois
Cairo is the southernmost city in Illinois, at the meeting of the Ohio and Mississippi Rivers. Huckleberry Finn and Jim plan to stop here, sell the raft, get on a steamboat up the Ohio to a free state.

Unfortunately, they miss Cairo, and their canoe is lost or stolen, so they cannot return upstream without proceeding further downstream to get another canoe. As they set off downstream, their raft is hit by a steamboat and they are split off from one another; alone, Huck asks for help at the first house he sees; assuming the false name "George Jackson", he is taken in by the Grangerford family.