The full map, published in 1865 by Martenet and Bond, is available online from the Library of Congress:
https://www.loc.gov/item/2002620533/
Below is a section of the map with the approximate location of the current Riderwood campus highlighted. The county line appears to be offset somewhat in the map, and the orientation is not North/South, but rather North is at an angle. CLICK on the image to view it in a new window, where you can scroll and zoom to view areas of the map.
