A little over 100 years ago, my wife’s great grand father found this mortar and pestle while plowing their field located in Christian County Kentucky. Their family farm has been there since the late 1700’s. Both my wife and her mother are interested in finding out if anyone can identify it based on the photos located here:
This area was primarily occupied by Shawnee Indians as well as Cherokee Indians; also this area of Christian county is on the Northern route of the Trail of Tears, so it may not be Shawnee or Cherokee. We have found very little in our research and hoping to find out a little more.
You can try asking this at /r/AskAnthropology for more exposure. Material culture like this really is the purview of archaeology, which is a sub-discipline of anthropology.
Unfortunately I am not very familiar with the archaeology of that region. I will note that ground stone objects like this are much harder to interpret than other material types (because they often don't have a very distinctive style), but in this case both the mortar and the pestle are quite distinctive, so you may have some luck.