Many of the forest service CG stay open here in Michigan, mainly to cater to hunters... don't expect plowed roads or sites, but if you can get in, and get out, you can camp there, for free usually.
The 4th season is 6-7 months in my area, excluding it from camping wastes a lot of calendar.
I load up extra propane, extra generator fuel and head out and enjoy. When the snow gets too deep for rustic camping, several State parks plow their roads and open a handful of electric campsites...
Nothing beats the silence found in winter camping.