Harold Heiden Koster was born September 7, 1917 in Dundee, Michigan as the third child of Lena (Heiden) and John Koster, Jr.

He was a 1936 graduate of Dundee High School.

On January 23, 1938, he married Violet E. Keck at St Matthew Lutheran Church in Raisinville Township, Monroe County, Michigan. and they lived at 7763 Summerfield Road in Lambertville, Michigan a few miles north of Toledo, Ohio. They had no children.

Harold died on June 14,1984 at the age of 66 and is buried at Maple Grove Cemetery in Dundee. He was preceded in death by his wife, Violet, who died on March 14, 1973 and is also buried at Maple Grove Cemetery. She was 52 at the time of death.