It's not so easy to you know you are there. You can park at Pavillion #7 in the back, east end. Follow the tags now. You are not supposed to ride the old river trail which is hiking only.
How to get there:
Take I-95 to the Stuart exit and go north to Lost River Rd. Or, take SR 76 to Lost River Rd. Follow the signs to the park. Go all the way to the back, we usually ride from the parking by Pavillion #7.
Ride around the triangular shaped retention area and look for a big metal gate. There's singletrack which bypasses it to the right. Enter there, ride to the first 'road' hang a right and look for the tagged trail to your left.