The RV parks are kind of few and far between up here in central Wisconsin. Normally we stay at Lake Wissota State Park in Chippewa Falls and I highly recommend that to anyone in the area. I wanted to try something new this time so we're staying at McMullen Memorial County Park in Warrens.
It's a first come first served, self-register park with electric only hookups. The layout is a little odd, with quite a few of the sites being "2+" unit designated, but overall the sites are large and fairly easy to get into. You can't beat the price - we paid $110 for 7 nights in this giant site with electric and water.
There is a nature trail that goes through the woods and past the roomy tent site area. It loops around the giant rock "mound", and has a spur trail that goes deeper into the woods that we haven't investigated yet. Fishing seems to be a popular activity here, all the weekenders are down at the lake with their poles.
I didn't check out the shower area, but the flush toilet building was very clean and well maintained and there is a camp host and firewood for sale. Overall a very nice park that I would recommend. Warrens has an annual cranberry festival the last weekend of September, I'd say it would be hard to get one of these non-reservable sites at that time!