Wow. This is such a wide open request.
Wisconsin has many, many great places and campgrounds.
As others have said, the State Parks are great. Devil's Lake SP is a real treat and there are several other state parks nearby that you can day trip to. Be sure to eat at the Ishnala Supper Club in Mirror Lake State Park. The setting and the food are wonderful!
Also, lots of National Forest campgrounds at the two NFs in Wisconsin - Nicolet and Chequamegon National Forests.
It all depends on what you want to do and how you want to camp. Whatever you do, there are lots of State, County, National Forest and private campgrounds to host you.