1. Just take 206 South (RIGHT out of either of Rider's entrance/exits).
2. Make the first left onto Darrah Lane.
3. Follow Darrah Lane (and E. Darrah Lane) almost to its end at Rt.1 and make a LEFT turn into the Mercer County Library Parking lot. (Google Maps wants to take you around the corner on Allen Lane to Rt. 1, since the address is officially on Rt. 1, but this is unnecessary. You can access the parking lot from E. Darrah Lane.)