What is the oldest American picture book still in print?

The oldest American picture book still in print is Millions of Cats.

Written and illustrated by Wanda Gág, the book was first published in 1928 by Coward-McCann. Its simple, hand-lettered story follows an elderly couple who feel lonely and ask the husband to find a cat. He returns with an enormous procession of cats—“millions and billions and trillions” of them.

The book's unusual visual style reflects Gág's work as an artist and printmaker. Its black-and-white illustrations and rhythmic text helped establish it as an enduring American picture-book classic. Gág's brother helped with the hand-lettering.

Millions of Cats received a Newbery Honor in 1929, making it one of the relatively few picture books recognized by that award. Readers sometimes confuse “oldest American picture book still in print” with the oldest picture book ever made; the claim specifically concerns an American work that remains continuously available in print.