It shouldn’t be too hard to peruse Chicago newspaper records for that year. A story like this would certainly have made the news. I no longer have a subscription to Newspapers.com or I would look.
Perino found them in 1948... so someone could have spread the stories after hearing about his find, a lot of folks from that era in Illinois were into Indian artifacts and legends in a big way.
The Alton Piasa bird is a combination of real bluff paintings of the American Indian “underwater panther” described by the explorer Marquette as being painted by whirlpools in the river possibly to alert travelers, carvings found on Spiro mounds Oklahoma cups or gorgets, and imaginary details invented by a newspaper contributor a long time ago influenced by European dragon tales - his story sounds more like Tolkien’s story about the dwarves and Smaug. The creater Alton has painted on the bluffs doesn’t resemble the originals copied by Marquette very much.