In Mississippi, you can ride ATVs on private property at the property owner's discretion. In addition, you can ride an ATV at some state parks. The park must have a waiver on file for all ATV users ages six to 21. Mississippi has several ATV parks and designated trails throughout the state, such as Red Creek Off-Road and Up the Creek Acres.
Check out these Grenada, MS ATV/OHV resources:
