A permit is required and I have one. The permit covers most MO. State parks but only for beaches and only between the hours of 7AM-9AM which leaves me scratching my head. It is for those reasons that I have not detected in any of those parks.
Missouri
http://www.mostateparks.com/
Metal detecting is allowed only on specific sand beaches in the facilities listed below. A permit is required and may be obtained free of charge by writing to Missouri Department of Natural Resources, Facility and Visitor Services Program, P.O. Box 176, Jefferson City, MO 65102, or by e-mail.
o Crowder State Park
o Cuivre River State Park
o Finger Lakes State Park
o Lake of the Ozarks State Park
o Lake Wappapello State Park
o Lewis and Clark State Park
o Long Branch State Park
o Pershing State Park
o Pomme de Terre State Park
o St. Joe State Park
o Stockton State Park
o Trail of Tears State Park
o Harry S Truman State Park
o Wakonda State Park
o Wallace State Park
o Watkins Woolen Mill State Park and State Historic Site