Location: Yes, you're still in Indiana, but just barely. Take SR 727 west from I-69 and you're there, just like that. Don't miss the exit or you'll wind up in Michigan.
Description: The attraction here is supposed to be winter sports and the Pokagon Inn (which I have stayed at--it is in fact very nice). There is a huge toboggan run. It isn't bad in the non-snowy months, either; there are a couple of very nice trails, including the Bluebird Hills Trail and a trail that leads through the Potowatomi Nature Preserve, which is within the boundaries of the park. This is a very popular park, so the usual cautions about trying it on weekdays apply; but there is no off-season for this park, so go anytime of year and try to miss the weekends. For more info and some photos, check out this Field Report from Mark Tarrant.
Nearby Points of Interest: This county is packed with natural areas, including Cedar Swamp, Little Grass Lake, Beechwood Nature Preserve, Loon Lake, Marsh Lake, McKenny Nature Preserve, and Ropchan Wildlife Refuge. Can it be that there's a county government in Indiana that gives a damn about the environment? Also see Pigeon River Fish and Wildlife Area, which contains two more nature preserves.
Cautions: This is a popular winter park because it snows a lot up here. A real lot.
Ownership: Indiana DNR