Madison was not listed as living with his mother Sarah in her divorce proceedings in 1857 - neither was Benjamin who is known to have been married by that date. Either he had married, moved away, or died. His name was clearly "Madison" in the 1850 census.
In 1860 in Madison Co, living two doors from Benjamin Dennis was "Matthew" Dennis, listed as age 22. His wife was Flora Dennis and is reported to have been Flora Thaxton, sister to Rhoda Thaxton who married the eldest brother Richard. She was listed as being age 26. There were three children: Martha age 6, Calvin 2, and Blake 2. If Matthew, or Madison, was the father of these children, he would have been only about 14 when Martha was born. The 1850 census gave Madison as being age 15, or born about 1835 which would have made him about 25 in 1860 and then he would have been about 19 when Martha was born - much more reasonable.
The 1870 census provided a clue to his name. This time he was listed as "James" Dennis. Probably named for President James Madison. His family was living in Seminary Precinct, Hopkins Co, Kentucky, p.142, Hh 142.
1850 Census, Jackson Co TN, District 12, Hh 550
James Madison DENNIS and Flora THAXTON had the following children:
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