Here is more info on John N. Rentfro:
He served in the Civil War from Illinois and applied for a pension from Missouri.http://interactive.ancestry.com/4654/32959_033055-02284/1187...
The actual pension file should have loads of good information. Note that Margaret L was his widow. So this might be a 3rd marriage.
Here is the 1890 Veterans census for John.http://interactive.ancestry.com/8667/MOM123_30-0550/282895?b...
This confirms that the John from Jasper Co MO is the same one whose pension card is given above.
I located John and Margaret in the 1900 census, in Newton County, MO. They had been married for 15 years (c. 1885). http://interactive.ancestry.com/7602/004118806_00218/3010524...
John was a preacher.
So the info on Margaret L as John's wife was correct. But she was his 3rd wife, which is probably why there was a separate grave. John likely bought the plot for him and his wife Sarah when Sarah died in 1884.
If you contact me via Member connect and give me your email, I will send you a copy of Margaret Rentfro's death certificate.
I urge you to get John's actual pension file. It should supply you with confirmation of the above and lots more.