Erlin John Koster was born in Ida, Michigan on February 1, 1904 as the first child of Lena (Heiden) and John Koster, Jr.

He married Helen M. Schaefer on February 9, 1924 in Dundee, Michigan. They had two children and started their married life at 303 Goodale Ave in Toledo, Ohio. By 1935, they were divorced.

On January 9, 1936, Erlin married Helen "Wava" (Dorell) Hazlet at St John Lutheran Church in Dundee, Michigan. From 1945 to 1965, they owned and operated Hopewell Grocery store in Toledo.

After retirement, they moved to Bedford Township, Monroe County, Michigan which is where Erlin died at the age of 80 on October 8, 1984. He was buried at Maple Grove Cemetery in Dundee. He had 3 grandchildren and 8 great grandchildren at the time of his death.

Wava who was born on August 23, 1911 in Lyons in Fulton County, Ohio died on January 7, 1983 in Toledo Hospital in Toledo. She was 71 years old and is also buried at Maple Grove Cemetery.