After his mother’s death in 1913, the family left Washington and returned to Sweden where his father married Elsa Viktoria Larsson.
Olsson married Dagmar Theodora Gavert on June 15, 1940 in Cook County, Illinois.
Olsson enlisted in the United States Navy shortly after the attack on Pearl Harbor.
Olsson wrote numerous articles, monographs, and other academic papers, dealing mostly with Swedish immigration and genealogy.
After twenty years of research, his work, Swedish Passenger Arrivals in New York, 1820-1850, was published by the Royal Library in Stockholm in 1967.