The postcard was sent to sisters Pauline and Theresa Leisenring in Elmira, upstate New York from Rockford, Illinois.
The Huffington Post reports that the postcard was sent by the pair's parents after visiting their son George.
George Leisenring was in the state due to being stationed at Rockford's Medical Centre Barracks in Camp Grant, an army post during World War II.
The message was sent home to the two girls and reads: "Dear Pauline and Theresa, We arrived safe, had a good trip, but we were good and tired."
An official from the US Post Office says the postcard was likely found by someone outside the postal service and placed in the mail recently.