Throughout this vicinity you'll notice the Historical markers commemorating Sybil's famous ride, awakening all the local militia to muster and march towards Danbury to save the town from the impending British invasion.
The posted coords are that of her actual gravesite.
Once you complete the nearby Adventure Lab showing you some of the stops along her route, you'll be given coords to help locate this bonus cache in her honor, placed in a very approprite location.
You can follow this link to the Adventure if you like:
https://labs.geocaching.com/goto/Sybilsride