Much is known of John Jacob, Sr., 17th century Maryland immigrant, but nothing of his origin other than he likely arrived in 1661.  There are about fifty direct and indirect references to John in documents that are preserved in the Maryland Archives.  They refer to his early years in Anne Arundel County as an indentured servant and afterwards a freedman that patented land, married, prospered, and fathered children who in turn left numerous descendants that trace their lineage to him today.  Many are members of this project.  However, no record survives of John’s entry to the Maryland scene or his origin.  Thus, Y-DNA testing becomes a potent genealogical tool in two important areas: first to verify or identify his direct male descendants and second to predict or determine John’s origin by identifying genetic matches between his descendants and other families that trace their lineage to the Old World.

In typical 17th century fashion, John signified his name using a monogram of his initials; in a stylized opposing 'J' form appearing thus: JI.  Period documents show variant spellings of his surname: Iacobe, Jacob, Jacobs, Jaccobs. The addition of the 's' to the surname has no significance and merely reflects a characteristic spelling shift that occurred in many English surnames during the 17th and 18th centuries.

John’s 1719 last will & testament and the All Hallows Parish Register together provide the identities of John’s ten children that Anne, his wife, bore to the family.  Four sons, John, Jr. (C.1680-1740), Joseph (C.1686-1773), Benjamin (1688-1758), and Richard (1697/8-1779) produced offspring and direct lines of male descendants that can avail themselves of Y-DNA testing to confirm their ancestry.