Twain called Huck's home town "St. Petersburg", but it the city was truly based on Hannibal, Missouri.
Hannibal was a tiny town when Twain lived there. Explorers found salt in the area, in the late 1700's. Salt was very important for a lot of purposes, so the area was popular. The city itself was founded in 1819. By 1830, the population had increased to a frantic 30 (thirty) whole people! In 1840, the population was about 1000 This was about when the book is set. By 1850, the population was up to about 2000. Not a bustling community, but not a total tidewater either.
In addition to the aforesaid salt, the industry in Hannibal consisted of pork packing, soap and candle making, coopering, lumber milling, grain milling, rope making, and tanning. Pretty much what you'd expect from a river town.
Hannibal wasn't really close to any other larger towns, so it would have been pretty insulated, except for the river traffic and traders.
Unlike a lot of other small towns of that era, Huck Finn would have seen and appreciated the river as a way to get to more exciting areas.