Polk County didnot come into existance until 1835 which would tell me it was very sparely populated. If someone died they didn't have undertakers it was up to the family and any friends that lived close enough to help with the burial. The women would wash and dress the body and the men would dig the grave. Their cemtery would be some site on their land and it would become to be know as the Coffman Cemetery. Until Missouri passed a cemetery law these family cemeteries would be plowed up and they would disappear from the records and any ones memory. You haven't daid when your cousin found the cemetery. If it was rescently it should still be there but if it was some time ago there is a chance it has disappeared. I have looked at everything I could think of trying to locate this cemetery but no luck. I found who I think is a son of David, James L Coffman according to his deth certificate he was born Jan 9 1835 in Granger Co TN and he died June 9 1921. He is buried in the Pleasant Ridge Cemetery. I looked at a very early plat book and did find a Coffman owning land in the general area of your directions for the cemetery. I would have bee willing to go look for this cemetery but I live in the NE part of Missouri. Good luck.