Private Hironimus was a member of the 32nd Infantry Regiment, 7th Infantry Division. He was Killed in Action during the regiment's assault on the southeastern edge of Seoul, South Korea, on 26 September 1950.

Hironimus was awarded the Purple Heart, the Combat Infantryman's Badge, the Korean Service Medal, the United Nations Service Medal, the National Defense Service Medal, the Korean Presidential Unit Citation and the Republic of Korea War Service Medal.