Since you are looking to be along THE River keep the Corps of Engineers in mind. We stayed at a very nice CG just a bit south of Chamberlain at Yankton. Beautiful sites, many waterfront and you'll find the price is right too. Check there website to see if any closer to where you're planning to be.
Roger in NJ
" Democracy is the worst form of government. Except for all the rest"
Winston Churchill 1948
TAC - NJ 18