This may be a "wild goose chase", but I have a gg grandmother Elizabeth (maiden name?)who was my great grandfather's (John Robert Allen) mother. I think his father was John Allen (b.1846 - d?1878)from Knox Co. Missouri, but I have not been able to confirm this father-son relationship. John was the son of Robert O. Allen from Knox Co. MO. and disappears from the census rolls between 1870 and 1880. He may have been a law-man who died somehow. My Elizabeth had three children from 1873 - 1878 (John Robert, Myrtle, and Albert). I don't know what happened after 1880 with her. Any of this fit?