We need good camping places, Mississippi river valley

Not knowing your route, and you mentioned the Mississippi River, Lake Chicot State Park is in the lower eastern part of Arkansas just across the river from Greenville, MS and I believe a bit north of Grand Gulf Military Park, MS. Chicot is nice, nothing to write home about, but for a stop over, we liked it very much. And we did actually from there head to Grand Gulf Military Park, but did not stay there.
Hope this helps.