As mentioned, there's an excellent network of trails throughout the USA. Some, like the Katy Trail cover long, cross state distances.

Otherwise, throughout the country, especially in areas that were developing before cars were ubiquitous, there are plenty of nice, relatively quite, 2 lane roads. Consider anywhere in the northeast, outside on the major cities on the coast. Also, the Texas hill country west of Austin, most of Illinois and Ohio south of the great lakes, most of Michigan, and your home state of Wisconsin all offer excellent bike touring possibilities.

I don't know where exactly you live, but I'd start with a weekend in the Dells.