The statues were stolen from the library's courtyard sometime around May 31, WLS-TV, Chicago, reported.
The two works, one titled "Imagine That," which portrayed a young girl sitting on a stack of books with a soccer ball nearby, and the other, "Little Scholar," with a figure of a boy engrossed in a book, were valued at a total of about $15,000.
Police said in order to abscond with the statues, the thieves had to chip away the stone bases, which were bolted into concrete.
They were among 11 statues placed in the library's courtyard as part of a project called "Art of a Story" in 2000.
Library officials said the stolen pieces were insured.