Now, a couple of these are "sorta cheating", as I've never stayed in South Dakota, but I did spend a day there, playing slots at an Inidan Casino and having lunch at a mall (in Sioux Falls ... we were vacationing in Pipestone, MN), so I guess it counts for "visiting" ... same thing for Iowa, I spent a day looking at Indian Mounds on the Iowa side of the river (just north of Dubuque, if I recall correctly), but was actually staying on the IL/WI side.
create your own visited states map
or write about it on the open travel guide