He stayed with families in both Bensenville and Elmhurst before enlisting.
The Daily Herald says Marine officials tell them Pietrek joined the military as a way to speed up naturalization.
More than 35,000 servicemen and women have been naturalized since September 11, 2001.
Pfc. Pietrek died Saturday while supporting combat operations.
He was assigned to the Marine base at Twentynine Palms California.