There used to be some in the Driftless area but not sure any longer. There were also some in the Northern Kettle but I haven't seen one there in 40 years.I have seen a reasonable number while driving on the atv trails around Black River Falls. I believe some of those trails run through state forest. Never hunted it as I stick pretty far north, and I think even for a 2 day trip I'd make the extra drive. But I do think you'd find some in that area.
Not exactly Southern, but a couple hours South of what might be considered prime grouse range.