John E. Grabosky was born on February 15, 1919 to John and Petronella Grabosky of Chester, Delaware County, Pennsylvania. (On an official form, there was some confusion about whether John was from Chester County, or Chester City) John was the oldest of three children. The family moved to Minersville, PA where his father worked in a coal mine.
John graduated from high school. After graduation, he entered into the Army Air Corps on September 10, 1940. He was discharged on September 24, 1945.