I had a folder on my desktop that I dragged to the dock next to my Documents folder and it is now located there. I deleted the original folder on my desktop and the folder in my dock remained. Where is the folder in my dock now saved to?
Since you deleted the folder, it is now in your Trash.
Empty your trash and it will be... nowhere, the data will be lost.
The icon will remain in the Dock, but when you click on the icon you will get a question mark :
Of course, if you do NOT want to loose this folder, do not empty the Trash...
When you drag a folder to the Dock, you do not move it : the folder does stay in its place.
Therefore, the answer to this question : "Where are folders placed in dock saved to?" is : these folders did not move, they still are at the same place.