HARRY MAILAHN was born on June 17, 1926 to William Harry Mailahn and his wife, the former Florence Cummiskey. 

The 1927 and 1928 City Directories shows the family residing as 1117 Lawrence Street. William Mailahn was working as a driver. The 1930 Census shows the family at 1015 Lawrence Street, with William Mailahn working as a driver for an ice company.

The 1940 Census shows the family, which included older siblings Anna and Louis, and a younger brother, Albert, living at 3108 River Avenue in Cramer Hill. William Mailahn was then working as a deckhand.

Harry Mailahn served in the United States Navy during World War II. He returned to Camden and married Evelyn Winner. A son Harry Jr., was born in October of 1949. In May of 1950 Harry Mailahn took the Civil Service test for a position on the Camden Police Department. In October it was announced that he was one of seventy-seven who passed. He successfully tested for the Fire Department around the same time. The Mailahns were then living at 405 Beideman Avenue, in the Westfield Acres public housing project. They were still at that address when, on January 16, 1951 Harry Mailahn was appointed to the Camden Fire  Department. He was soon assigned to Engine Company 9. They had moved to 243 South 32nd Street by April of 1953.