Spencer Pettis was born in [[Culpeper County, Virginia]], to parents John and Martha (Reynolds) Pettis in 1802.<ref>{{cite web|url=http://archiver.rootsweb.ancestry.com/th/read/PETTIS/2002-03/1016829138|title=Pettis Archives|publisher=Rootsweb.ancestry.com|date=22 March 2002|accessdate=19 July 2012fact}}</ref> His father was a veteran of the American Revolution, serving with the 1st Regiment, [[Virginia Line]] at the [[Battle of Guilford Court House]] and elsewhere.<ref>{{cite web|url=http://www.virginiafamilytree.com/2007/11/john-pettis-of-spotsylvania-county.html|title=John Pettis of Spotsylvania county|publisher=Virginia Family Tree.com|date=5 November 2007|accessdate=19 July 2012fact}}</ref> Spencer Pettis' exact date of birth and much about his childhood is unknown. Genealogy records indicate he did have at least two sisters, one of whom, Sally, was the mother of [[American Civil War]] naval officer [[Thornton A. Jenkins]]. Spencer Pettis received at least enough education to study for the law and become a practicing attorney. Pettis moved west in 1821, settling in central Missouri's Boonslick region, opening a law practice in the [[Howard County, Missouri|Howard County]] seat of [[Fayette, Missouri]].<ref name="Christensen">Christensen, Lawrence O.,''Dictionary of Missouri Biography'', University of Missouri Press, 1999</ref>
