On July 4th, 2015, I went to the Old Burying Ground in Harvard Square, Cambridge, Massachusetts for two reasons. First, to locate stones of my newly discovered ancestors, William Manning and his wife Dorothy, and to find the stone for Mary Prentice Balch. I was able to locate both, because of photos I had as a guide.
If I don't know where somebody is buried, the first thing I do is go to www.FindAGrave.com and put in the persons name and other data, if known. Often there will be a photo. In the below picture on the FindAGrave site, you can see a rather tall stone on the back right (behind Mary's stone). This clue made my search rather easy. You need to remember, they can look different, depending if the photographer is sitting, kneeling or standing.
Here lyes buried ye
body of Mrs. MARY
BALCH, wife to Mr.
who departed this life
Janry. 28th Anno Dom. 1741in
ye 64th year of her age.
Her siblings, Elizabeth and Nathaniel were also buried here.