The Mississippi River along Missouri, Illinois, and Arkansas sometime in the 1830s-40s.
It’s important to understand the context of Huck’s world to see what’s going on in the novel.
Adventures of Huckleberry Finn takes place roughly twenty years before the U.S.
Civil War. Slavery is still legal, common, and socially accepted in the South. This is why Huck struggles so much with helping Jim escape – everything he knows tells him this is wrong legally, morally, and socially. It’s enough to drive a kid to three – maybe even four – moral crises en route. As far as the geographical setting goes, you’re looking at river towns and the simple folk that live there. The people Huck encounters are for the most part uneducated, superstitious, kind, and hospitable, but that’s just the novel’s environment.
Now take a look at the smaller scale – the actual places Jim and Huck go on their journey. It’s interesting to note that the pair starts off moving in a linear fashion, both geographically and metaphorically. They have a singular destination:
Cairo. This is fairly straightforward, as is Huck’s initial rationale for freeing Jim. However, as Huck begins to suffer in moral limbo, so does their journey. The two of them miss Cairo and end up running from one set of troubles to the next, especially once the duke and the king come into the mix. Clearly, their journey – and the novel’s path – isn't as simple, linear, or goal-oriented as we thought.