Get a plat book and contact your nearest WDNR office. Ask them for a list of all of the MFL (Managed Forest Land) properties in your area. These are similar to the CFR properties in Michigan that the previous poster alluded to. Most land under MFL is open to the public for hunting, but because it's privately owned it's still good form to talk to the landowner to let them know you're hunting there (to be polite...they cannot refuse you though). Treat it like public land though...not cutting trees, permanent stands, etc.

Also check out the Nicolet NF, it's not too far from you IIRC.

Good luck this season!

Edit: Permission is most certainly required in WI to hunt private land, but as a WI hunter you already know this.