The Gandy Dancer trail is open for <abbr title="All-Terrain Vehicle (ATV)">ATV</abbr> use in MN and you can get on the trail in Danbury. The WI Burnett Co. portion is not during the spring, summer and fall. In winter it is open to snowmobile and <abbr title="All-Terrain Vehicle (ATV)">ATV</abbr>.
As Dave S. suggested joining a club is a great way to gather information as you mentioned it varies by county, township and city.
Safe Adventures!