Madison's parents appear to be George Rock Jr. (1788-after 1860) and Betsy McCoy (before 1800 -?), married on Nov. 11/13, 1811 in Botetourt County, VA, so Madison looks like a first anniversary present. George was the older brother of my Gr-gr-gr-grandfather, Jacob Rock. Their father appears to be George Rock Sr., apparently born in PA sometime in the 1750s and his wife's name was Eve (according to a death certficate for their daughter, Elizabeth). It appears that both George Jr. and Elizabeth may have been widowed (she definitely was) since it appeared the two of them lived in the same house according to the 1860 census.
The trail is cold right now beyond George Sr. I have him on tax rolls in Botetourt in 1789, 1794, 1799, census data from 1800, 1810, 1820, and 1830, several listings at the marriages of his children, plus a contract to buy 144 acres of land in 1788 along a spring off the James River.
I hope that this answers your question and helps. Any idea why Madison travelled west? Was he a soldier?