In 1953, during his first trip away from his Illinois home, Alan Ball sent his family a postcard from the United Nations headquarters in New York, the postage for which was 2 cents.

Mr. Ball, who was in high school at the time, bought the postcard on his way to Puerto Rico, where he planned to spend the summer at his aunt’s home. He had taken a train to New York, and visited the U.N. in his spare time before his flight to Puerto Rico.

“We are now in the U.N. bldg. — extremely modern throughout,” he wrote in neat cursive on the postcard, which displays one of the U.N. headquarter buildings on the front. He promised to “write next from P.R.” and signed it, “Love to all, Alan.”

But the postcard never arrived at his family home in Ottawa, Ill.

Mr. Ball, who is now 88, had “totally forgotten” about it until Wednesday, when a letter carrier handed it to him in Sandpoint, Idaho, where he has lived for more than 30 years.

“That 2 cents did a lot of work,” said Mr. Ball, a retired emergency room doctor, during a phone interview on Saturday. “It has mostly brought a chuckle to me because, you know, who gets their mail returned after 72 years?”

The postcard, an update from Mr. Ball on his travels, provided the kind of quick message one might send in a text or a social media post today.

In addition to describing the modernity of the U.N. headquarters, the dispatch details how Mr. Ball had yet to buy a ticket for his flight, but “will see about it pretty soon.”

It also mentions a telegram Mr. Ball had received from his family on the train, to which he replied, “think all will be OK.”

It was addressed to the Rev. F.E. Ball, Mr. Ball’s father, and his family, and dated June 17, 1953, complete with a U.N.-branded stamp.

Its faded front shows the towering U.N. Secretariat Building against a bright blue sky. In one corner, the turquoise water of the East River peaks out from behind the building.

Mr. Ball doesn’t remember much about his trip to the U.N. or time in New York, but when he saw a photo of the faded message, he immediately recognized the handwriting as his own.

He never knew the postcard wasn’t delivered, and never thought to mention it to his family.

“There wasn’t anything important in it,” he said. “It just said, ‘Here I am, and I’m kind of just hanging out,’ I guess, ‘and waiting for the airplane someplace in New York.’ Of course, I was never out of the State of Illinois before this trip, so it was a big deal for me.”

Last month, the postcard abruptly surfaced at the Ottawa Post Office in Illinois.

Postal officials said they believed it had spent most of the past seven decades lost in the U.N. and had only been mailed recently, The Shaw Local, a newspaper in Illinois, reported.

The town’s postmaster enlisted help from several genealogists to match the postcard to Mr. Ball more than 1,700 miles away.

“They did some sleuthing and found out I was here in north Idaho, and the next thing I knew, I was getting a call from a reporter back there,” Mr. Ball said.

Since then, he’s become somewhat of a local celebrity in Sandpoint, a city of more than 10,000 people about 70 miles northeast of Spokane, Wash. He posed for a photo with the mail carrier who delivered the postcard, and his story appeared on the front page of The Bonner County Daily Bee, a local newspaper.

Though he doesn’t recall much about his visit to New York, memories of Mr. Ball’s summer in Puerto Rico remain vivid.

He remembers the constant drone of the propeller plane that flew him there, and how even the horses understood Spanish better than he did. He recalled tasting coffee for the first time on the small plantation his aunt and uncle ran in the mountains and painting the barn where they treated the beans.

Even though it arrived 72 years late, Mr. Ball now has a new way to commemorate those formative summer travels. He plans to frame the postcard and hang it on a wall in his home.

“I like the unexpected, and I like fun stuff,” he said, “and this had both.”