I am taking my wife and kids on a roadtrip next summer to my sister-in-law's in Wisconsin. Obviously we will be hitting up several destinations in the mountains but the plains are a different matter. What we'd really like to do is camp somewhere on the plains that has a wild character. In an ideal situation, we'd camp out at Agate Fossil Beds or the Tallgrass Prairie, but neither have camping. We don't want farms, we want grassy, wind-swept expanses. We'll be heading east through Nebraska or Kansas and back through South Dakota. I'd prefer to camp somewhere in the former, since we plan on biting off Wisconsin to Badlands in one long day. Any ideas? Thanks!

There are lots of opportunities for "unofficial" camping out in the plains. I have spent many nights in the CO/WY/NE/SD/KS plains camping right off the side of rural backcountry roads without problems. Many of these spots have been in areas you are seeking out; "wild", open, not on a farm, etc. Seeing as you'll be with your family, I can understand if that isn't the route you want to go for, but you will open yourselves to a lot more options if you are willing to camp unofficially, in the "dirtbag" style.

Pawnee National Grasslands in NE Colorado is alright. They have a couple developed campgrounds, and the same dispersed camping regulations you'd find in the national forest, so that's nice. The area does have a nice open feel to it, but honestly, with Fort Collins being only an hour away, you might find it not to be quite as empty as you'd like, maybe. There also have been lots of fracking activity in the area, so truck traffic might be a turnoff, though I think this has decreased in the past couple years. Here is a spot I've camped at before that's a little more removed from the area you'd find most people (4wd required), and is truly out on the open prairie, away from everything: https://goo.gl/maps/5AZDcEF886t

I've never been there, but the CO/NE/KS tri point looks like it would be a pretty cool place to camp at. Dirtbag style, of course.

The Sandhills of Nebraska are very wild and empty. You can really get a feel of old pioneer times out there. Unfortunately I don't believe there is any developed camping out there, but there are so many country roads that roam across the hills, camping along any one of them shouldn't be an issue, so long as you stay on the roads themselves. There is a place called Smith Lake off Nebraska Highway 250 in between Rushville and Lakeside where I've camped before. I don't think camping was technically allowed, but there were fire pits along the lake and obvious spots where people have camped before. This spot has the benefit of being next to a nice lake, but you can also hike to the top of a nearby hill and stare off into the endless expanse of Sandhills stretching out in every direction. We probably heard only one or two cars drive by on the highway during our overnight stay there. https://goo.gl/maps/jLmVc4oJCGu

Not sure if this would be too far south for your trip, but Monument Rocks in Kansas is a cool place to camp at (http://www.summitpost.org/monument-rocks/413591). Again, it's unofficial.

Badlands is good too, and I see you are planning on visiting there.

Some of the best experiences of my life have been roaming around in the plains and exploring random dirt roads looking for awesome places to camp for the night. Like I said, I've never had any problems just pitching a tent on the side of a country road out there. If you pick the right roads, you won't even see anybody. Best of luck on your trip and hopefully you won't get hit by a thunderstorm, rather, watch it roll across the plains from afar. Here are some shots of the spot I linked to in Pawnee Natl Grassland:

This is perfect. Thanks a bunch!

Many National Grasslands, and National Forests for that matter, have dispersed camping where you are allowed to drive off designated roads 300 feet to a spot to camp. I'd look into Buffalo Gap National Grassland, which is in the Badlands neck of the woods. It was the first Grassland to have a proposed Wilderness area, so some of it gets pretty remote.

If you were going through the Sheyenne or Little Missouri National Grasslands, I could send you GPS coords for some good spots, but I'm guessing they are out of your way a little.