watching to see if there is anything close since I am in Olathe but...
the 2 big places I know about are:
1. Kansas Rocks park 69 by Fort Scott
KS Rocks Park
Been there but didnt have cash to pay my way in. seemed like real nice people and a place that was set up specifically for offroaders. They do lots of fun events, including a Jeep 101 class on how to offroad that is full everytime its offered (2xs a year)
2. Tuttle Creek OHV park.
Kansas City District > Locations > District Lakes > Tuttle Creek Lake > Trails > Off Road Vehicle Areas
Been here a few times and had a lot of fun but some of the areas are for hardcore machines. Be careful with the water because some holes are dug extremely deep even though the hole is barely bigger than your Jeep.