The Wildcat Mountain Bike Trail is purportedly the best spot to ride mountain bikes in Washburn County. This is really the only true singletrack trail of any substantial size in the county. With recent additions, it totals about 19 miles in length of rolling trails. However, not all 19 miles is actual singletrack: there's a combination of dirt roads and ATV doubletrack here that's required to connect all of the pieces of singletrack together.
Most of the trails are rake-and-ride, which obviously doesn't create high-quality singletrack, especially with the low amount of traffic that this trail receives. That said, some of the older sections of trail that have been ridden in more have developed their own sort of flow, but don't expect to be whipping through these trails the way you might at the nearby CAMBA trail system.