An investigation is being carried out at the 17-month-old building to find out why the glass has cracked and who should pay for it.
Speaking to the Des Moines Register, the city attorney Bruce Bergman said: 'We believe it's a defect in the glass.'
The panes reportedly began to crack before the first book was even checked out of the library, and 28 have had to be replaced since the building opened in April 2006.
The building is wrapped in an energy-efficient glass and metal skin. A copper mesh is laminated between three sheets of glass, giving the two-storey structure its distinctive look.
Bergman added: 'It's no-one's expectation that all of the windows in the building are going to break or need to be replaced.'
Images by Holly McQueen/Des Moines Register.