Best week of my life was some 6.5 miles south of Deadwood. Camped out in a tent in a little campground. Little clear cold stream some 15 feet from the tent. Sheltered from the afternoon sun by a couple of big pines.
NE Corner of SD is not bad if you enjoy fishing. Watertown to Britton roughly. Pretty country, lots of little lakes and potholes. Not a lot of people, lots of wildlife. Normally the first 2 weeks of June is the time to be there. Has not gotten too hot yet, bugs not yet gotten bad.
I live in Fargo so I tend to play more over on the Minnesota side. Lakes are closer, have trees around them, Non-resident family fishing licence is only 70$.