We MO peeps had a thread about this in Feb. Hangers of MO State Parks Heads Up
I ended up calling the MO Parks Dept to verify the size of the tree straps they were wanting used as a few HF members were told it was 3 inches. Apparently there is no the state wide regulation, but they prefer 2 inch nylon straps, but suggested checking with the individual parks as they may have a different idea of what's appropriate. Also note, no one I spoke with at the Parks Dept was keen on the use of hammocks.
At the opposite end of the spectrum, the MO Conservation Dept has no regulations or preference regarding suspension and were very happy to discuss the issue. As long as camping is allowed, hammocks are allowed.