Career
Jacobus struggled to teach and stress the importance of a scientific method of using primary sources in genealogical research. This replaced the idea of oral traditions and acceptance of time-honored pedigrees as facts due to their age. He provided the first basics of proper documentation and citation for all genealogists.
While he endorsed the concept of eugenics he felt it was seriously lacking in the ability to properly trace bloodlines nor were those proponents of the field experienced enough in genealogical research or ability.
He established the New Haven Genealogical Magazine in 1922, which became The American Genealogist ten years later. He served as the periodical"s editor and publisher for 43 years until 1966.
Jacobus was the son of John Ira Jacobus and Ida Wilmot. His favorite hobby was charting the descendants of Spain’s King Ferdinand and Queen Isabella (Ferdie and Izzie as he called them), demonstrating that as serious as genealogy had became for him, it was also bound up in fun and fantasy.".