The first data that I have is that Reuben Alexander m. Mary Garrison on 6 May 1794 in Cabarrus County, North Carolina. Hezekiah Alexander was bondsman and John Simianer was witness.
He was the son of William Alexander who was born 30 Jan 1745 - some say in Anson County, North Carolina, but more likely in Cecil County, Maryland.Reuben's mother was Esther (or Easter) Brown who was b. 23 Sep 1745.
William died 31 May 1820 in Maury County, Tennessee and Mary died 17 Oct 1823 in the same place. They are both buried at the Ebenezer Presbyterian church Cemetery (also known as Reese's Chapel).
This Alexander family is thought to have moved to Tennessee in the early 1790s. I wonder if that was after Reuben married in Cabarrus County in 1794? There may be records in Cabarrus that would show when William sold his property there in preparation for moving west.
They settled first in Sumner County but later moved to Maury County. Reuben may have moved to Smith County and I also show a Reuben in Kentucky.
The children of William and Esther (Brown)Alexander were:
1)Daniel Alexander b. 9 Jul 1767 2)Reuben Alexander b. 11 Dec 1768 3)Prudence Alexander b. 1 Dec 1772; d. 20 Jun 1845 5)Silas Alexander b. Sept 1777 4)Peggy Alexander b. 27 May 1800 6)Esther Alexander b. 14 Mar 1781 7)Absalom Alexander b. 12 Jul 1783; d. 24 Aug 1847 8)Alexander Brown Alexander b. 2 July 1787 9)Priscilla Alexander b. 12 Oct 1788
The record of the children of William and Esther came from "Alexander Kin" by Charles C. and Virginia W. Alexander, page 33. There is more information - if you like. There is also more on the ancestry of William although nothing on the ancestry of Esther - not even the identification of her parents.
Do you know where your ancestor, Reuben Alexander, went after he left his parents' home? Is he the one in Smith County? Did he go to Kentucky - and then to Missouri?
I would be interested in anything you have on the later years of your Reuben.