Right after I sent the first message, I found more record of Jefferson and Mary Mosby as well as a death record for their son, Powhatan Mosby (mentioned as living with Jefferson and Mary Mosby in Powhatan County on the 1870 census).
"Jeff" and Mary Mosby are found living in Manchester, Chesterfield County, Virginia on the 1880 census. With this at this time are their children, Junior Mosby (a.k.a. "Junnie"), Powhatan Mosby and Mary Saunders, who is 80 years old on this census.
The death record for Powhatan Mosby states that he was born in Manchester, Virginia (which I believe is actually the Manchester District of Chesterfield County, which is a neighboring county just east of Powhatan), and that his parents were Jeff and Mary Mosby. He died January 28, 1892 at the age of 26.
There is also record of a Jeff Mosby who died in Kentucky as well, but I don't know if this Jeff Mosby matches what you're looking for.
Feel free to contact me via email if you'd like-might be easier :) Email is firstname.lastname@example.org